Positive electrode for nonaqeous electrolyte secondary battery and a nonaqueous electrolyte secondary battery

ABSTRACT

There is provided a positive electrode for nonaqueous electrolyte secondary batteries having a high-density and a high folding strength. There is also provided a nonaqueous electrolyte secondary battery including such a positive electrode. The positive electrode has a high folding strength when it is used in a battery with a high current density, and a nonaqueous electrolyte secondary battery having such a positive electrode. The positive electrode has an electrode body having formed a folded portion at least at one part of the positive electrode. With respect to a cross-section of the positive electrode composition layer, a domain A extends from a central part to a surface side of a thickness direction, and a domain B extends from the central part to the current collector. The distribution of the binder in domain A and domain B are specified.

CROSS-REFERENCE TO RELATED APPLICATION

The application is a Continuation of U.S. patent application Ser. No.15/299,855, filed on Oct. 21, 2016, which is based on Japanese priorityapplication No. 2016-190602 filed on Sep. 29, 2016 and No. 2015-208433filed on Oct. 22, 2015.

TECHNICAL FIELD

The present invention relates to a positive electrode for nonaqueouselectrolyte secondary batteries having a high-density and a high foldingstrength, and a nonaqueous electrolyte secondary battery including sucha positive electrode. Also, the present invention relates to a positiveelectrode for nonaqueous electrolyte secondary batteries having a highfolding strength when it is used in a battery with a high currentdensity, and a nonaqueous electrolyte secondary battery having such apositive electrode.

TECHNICAL BACKGROUND

The nonaqueous electrolyte secondary batteries have a high volume energydensity and a weight energy density, and therefore, they have beenwidely used not only in consumer apparatus such as cell-phones andnotebook PCs but also in industrial application such as in-vehicle useand robot use. Therefore, the features demanded are diverse, and furtherimprovements in their performance are demanded by various means.

Patent Reference No. 1 proposes the followings. When a positiveelectrode composition layer has filled with particles of a positiveelectrode active material at a high density to be wound to form apositive electrode with a high density active material, a stress can begenerated to cause the current collector to be broken or the positiveelectrode to be damaged by making cracks or flaws in on the positiveelectrode composition layer. In order to restrain it, this referenceproposes considering a curve of a correlation between a distance fromthe current collector in the thickness direction of the positiveelectrode composition layer and a quantity of the binder. Then, theminimum point of the curve is made located at the central position ofthe thickness direction of the positive electrode composition layer.Also, this reference proposes providing the quantity of the binder atthe side of the current collector of the positive electrode at a highervolume than the quantity of the binder at a portion apart from thecurrent collector.

Patent Reference No. 2 proposes the followings. In order to obtain ahigh discharge capacity in a cycle at a high-speed charge discharge, atechnique is proposed to adjust the concentration of the lithiumelement, the quantity of conductive assistant, and the binder materialat a side of the surface of the positive electrode composition layer andat a side of the current collector.

Patent Reference No. 3 discloses as followings. In order to improve ahigh input output property and a charge discharge cycle characteristic,this reference proposes a positive electrode by providing two or morelayers of positive electrode composition layers, in which the quantityof the conductive assistant at the layer adjacent to the currentcollector is larger than the quantity of the conductive assistant of thelayers other than that layer adjacent to the current collector.

PRIOR ART REFERENCES

Patent References

Patent Reference No. 1: International Patent Publication No.2011-0148550.

Patent Reference No. 2: Japanese Laid-Open Patent Publication No.2011-129399

Patent Reference No. 3: Japanese Laid-Open Patent Publication No.2008-059876

The Objectives to Solve by the Invention

By the way, in order to improve the volume energy density, the foldingstrength of the positive electrode can be generally decreased if thecurrent density of the battery is set to be 3.85 mA/cm² or more. Also,when the density of the positive electrode composition layer is madehigher e.g. at 3.95 g/cm³ or more, the folding strength of the positiveelectrode can become low since the filling characteristic of thepositive electrode active material in a positive electrode compositionlayer is very high. Thus, when a nonaqueous electrolyte secondarybattery using an electrode body such as a winding electrode body of apositive electrode in which a folded portion is included therein, itbecomes likely that the positive electrode is broken at the foldedportion at the time of winding the electrode body or at the time ofcharging and discharging the battery, if a positive electrodecomposition layer includes a high-density positive electrode, or if thecurrent density of the battery is increased as explained above.

The objective of the present invention is to provide a positiveelectrode for nonaqueous electrolyte secondary batteries having ahigh-density and a high folding strength, and a nonaqueous electrolytesecondary battery including such a positive electrode. Also, theobjective of the present invention is to provide a positive electrodefor nonaqueous electrolyte secondary batteries having a high foldingstrength when it is used in a battery with a high current density, and anonaqueous electrolyte secondary battery having such a positiveelectrode.

SUMMARY OF THE INVENTION Means to Solve the Objectives

There is provided a positive electrode for a nonaqueous electrolytesecondary battery in which the positive electrode is to be housed insidean exterior body of a nonaqueous electrolyte secondary battery, thenonaqueous electrolyte secondary battery comprising an electrode bodycomprising a positive electrode, a negative electrode, a separator, afolded portion formed at least at one part of the positive electrode,and a nonaqueous electrolyte. The positive electrode comprising apositive electrode composition layer on one side or both sides of apositive electrode current collector. The positive electrode compositionlayer comprises at least a positive electrode active material, a binderand a conductive assistant. A density of the positive electrodecomposition layer is 3.95 g/cm³ or more. A cross-section of the positiveelectrode composition layer has a domain A extending from a central partto a surface side in a thickness direction thereof, and a domain Bextending from the central part to the current collector thereof. Thepositive electrode has an a/b value of 2 or more, the a/b value beingobtained in accordance with the method explained below.

Method to Obtain the a/b Value

It is to carry out a step of detecting elements derived from the binderby means of SEM-EDX with respect to the cross-section of the positiveelectrode composition layer. SEM-EDX can detect B (boron) to U(uranium). Among the elements detected, it is to carry out a step ofselecting a first element included in the binder at the highest quantityamong the elements detected, and selecting a second element included inthe binder at the second highest quantity among the elements detected.It is further to carry out a step of drawing a first element mapping ofthe first element, and drawing a second element mapping of the secondelement. The first element mapping is drawn in a vision field same asthe second element mapping. It is to carry out a step of calculating anarea where the first element mapping overlaps with the second elementmapping. The method is carried out on each the domain A and the domainB. A ratio of the area in the domain A is defined as “a,” a ratio of thearea in the domain B is defined as “b,” thereby obtaining the a/b value.

Also, there is another embodiment of a nonaqueous electrolyte secondarybattery. The nonaqueous electrolyte secondary battery comprises anelectrode body comprising a positive electrode, a negative electrode, aseparator, a folded portion formed at least at one part of the positiveelectrode, and a nonaqueous electrolyte. The nonaqueous electrolytesecondary battery has a current density of 3.85 mA/cm² or more. Thepositive electrode comprises a positive electrode composition layer onone side or both sides of a positive electrode current collector. Thepositive electrode composition layer comprises at least a positiveelectrode active material, a binder and a conductive assistant. Across-section of the positive electrode composition layer has a domain Aextending from a central part to a surface side in a thickness directionthereof, and a domain B extending from the central part to the currentcollector thereof. The positive electrode has an a/b value of 2 or more.The a/b value is obtained in accordance with the method explained above.

Furthermore, there is provided a nonaqueous electrolyte secondarybattery comprising an electrode body comprising a positive electrode, anegative electrode, a separator, and a nonaqueous electrolyte. Thepositive electrode is housed inside an exterior body of a nonaqueouselectrolyte secondary battery. The positive electrode comprising apositive electrode composition layer on one side or both sides of apositive electrode current collector, and a folded portion formed atleast at one part of the positive electrode. The positive electrodecomposition layer comprises at least a positive electrode activematerial, a binder and a conductive assistant. A density of the positiveelectrode composition layer is 3.95 g/cm³ or more. A cross-section ofthe positive electrode composition layer has a domain A extending from acentral part to a surface side in a thickness direction thereof, and adomain B extending from the central part to the current collectorthereof. The positive electrode has an a/b value of 2 or more, the a/bvalue being obtained in accordance with the method explained below.

In addition, yet another embodiment of the nonaqueous electrolytesecondary battery is provided. The nonaqueous electrolyte secondarybattery comprises an electrode body comprising a positive electrode, anegative electrode, a separator, and a nonaqueous electrolyte. Thepositive electrode is housed inside an exterior body of a nonaqueouselectrolyte secondary battery. The nonaqueous electrolyte secondarybattery has a current density of 3.85 mA/cm² or more. The positiveelectrode comprising a positive electrode composition layer on one sideor both sides of a positive electrode current collector, and a foldedportion formed at least at one part of the positive electrode. Thepositive electrode composition layer comprises at least a positiveelectrode active material, a binder and a conductive assistant. Across-section of the positive electrode composition layer has a domain Aextending from a central part to a surface side in a thickness directionthereof, and a domain B extending from the central part to the currentcollector thereof. The positive electrode has an a/b value of 2 or more,the a/b value being obtained in accordance with the method explainedbelow.

Effects of the Invention

According to the present invention, there is provided a positiveelectrode for nonaqueous electrolyte secondary batteries having ahigh-density and a high folding strength, and a nonaqueous electrolytesecondary battery including such a positive electrode. There is alsoprovided a positive electrode for nonaqueous electrolyte secondarybatteries having a high folding strength when it is used in a batterywith a high current density, and a nonaqueous electrolyte secondarybattery having such a positive electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view schematically illustrating thenonaqueous electrolyte secondary battery as an example of the embodimentof the present invention.

FIG. 2 is a perspective view of FIG. 1.

EMBODIMENTS TO CARRY OUT THE INVENTION

The positive electrode for nonaqueous electrolyte secondary batteries ofthe present invention has a folded portion at least at one part thereofwhen it is made into a battery. For example, the electrode body is awinding electrode body in which the positive electrode, the negativeelectrode and the separator, each being in a strip shape, are wound intoin an eddy form, and a cross-section of the electrode body is made intoa flat shape. The electrode body and the nonaqueous electrolyte arehoused in an exterior body to be made into a nonaqueous electrolytesecondary battery.

Positive Electrode

The positive electrode for nonaqueous electrolyte secondary batteries ofthe present invention (which is hereinafter simply referred to “positiveelectrode”) includes a positive electrode composition layer whichincludes at least a positive electrode active material, a conductiveassistant and a binder. The positive electrode composition layer isprovided on one side or both sides of a current collector.

The positive electrode, for example, can be prepared as follows. Thepositive electrode material, a conductive assistant, a binder and etc.are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) toprepare a composition containing a positive electrode composition in apaste or slurry state (here, the binder may be dissolved in thesolvent), which is then applied on one surface or both surfaces of acurrent collector, and dried, and then, a calendar process is applied ifnecessary.

In one embodiment of the nonaqueous electrolyte secondary batteries ofthe present invention, it has a current density of 3.85 mA/cm² or more.The current density means a value per unit area at the positiveelectrode at a current value of 1.0 C of the battery.

The followings are the reasons why the folding strength of the positiveelectrode is decreased when the current density of the battery is high.If the current density of the battery is tried to increase withoutchanging the density of the positive electrode composition layer of thepositive electrode, the thickness of the positive electrode compositionlayer should be increased. This, however, results in decreasing thefolding strength, and therefore, the positive electrode itself may bebroken when producing an electrode body including a folded portion atthe positive electrode (e.g., a winding electrode body having across-section being flat-shaped). On the other hand, in order to lowerthe current density of the battery without changing the density of thepositive electrode composition layer of the positive electrode, thethickness of the positive electrode composition layer should bedecreased. This may secure the folding strength of the positiveelectrode in part, but the area of the positive electrode compositionlayer has to be increased instead. Then, this results in decreasing thevolume energy density of the battery, and therefore, this is notpreferable.

In other words, if trying to realize a high capacity without reducingthe volume energy density of the battery, it will be a natural result ofincreasing the current density. Also, as a result of the examination bythe inventors of the present application, it was found that the currentdensity of the battery is 3.85 mA/cm² or more when the folding strengthof the positive electrode falls down in a case where the density of thepositive electrode composition layer is adjusted to such an extent thatthe battery has a high capacity.

In addition, in order to increase the current density of the battery, itcan be possible to adjust the quantity of the positive electrodecomposition (which will be explained later) applied on the positiveelectrode current collector at the time of preparing the positiveelectrode.

Also, when the density of the positive electrode composition layer ismade into a super high densely of 3.95 g/cm³ or more so that a rigidpositive electrode active material is highly filled, the positiveelectrode composition layer becomes very rigid. Then, at the foldedportion of the positive electrode, a load is applied from a portionwhere the positive electrode composition layer contacts the currentcollector, and finally the positive electrode itself including thecurrent collector may be broken. Even if breakage does not occur at thetime of preparing the winding electrode body, the positive electrodecurrent collector may be broken when charging and discharging thebattery because of exceeding its tolerance due to the expansion and theshrinkage of the negative electrode.

Therefore, the inventors have considered various ways to realize apositive electrode to restrict the breakage, even when the battery has acurrent density of 3.85 mA/cm² or more, or even when the density of thepositive electrode composition layer is at a level of a super highdensely of 3.95 g/cm³ or more. As a result, they have found theinvention by providing a positive electrode composition layer with ahigh folding strength if the binder of the positive electrodecomposition layer exists more at the surface side of the positiveelectrode composition layer rather than the current collector side.

When a large amount of the binders exists at the current collector sideof the positive electrode composition layer, that part becomes so rigidthat a load to the current collector is increased, and therefore, itbecomes more likely that the current collector is broken at the foldedportion. Therefore, by centralizing the binder in the surface side ofthe positive electrode composition layer, the load applied to thecurrent collector can be reduced, thereby preventing the breakage of thecurrent collector.

The analysis below can confirm the positive electrode in which morequantities of the binder exist at the surface side of the positiveelectrode composition layer rather than at the current collector side.With respect to the cross-section of the positive electrode compositionlayer, the elements derived from the binder are detected by means ofSEM-EDX (i.e., Scanning Electron Microscope/Energy Dispersive UsingX-Ray Apparatus). Among the elements detected, two kinds of the mostelement and the second most element in quantity are selected. An elementmapping is drawn for each element of the two kinds in the same field ofvision. The portion where each element mapping of the two kinds isoverlapping with each other corresponds to the portion where the binderexists. Thus, the area of the overlapping portion is calculated.

With respect to the cross-section of the positive electrode compositionlayer at one side of the current collector, a domain A extends from thecentral part to the surface side in the thickness direction, and adomain B extends from the central part to the current collector. An areaS is calculated for the portion where each element mapping of two kindsderived from the binder overlaps with each other. In the area S, a ratioof the area in the domain A is defined as “a,” and a ratio of the areain the domain B is defined as “b.” The positive electrode has an a/bvalue of 2 or more, thereby allocating the binder of the positiveelectrode composition layer more at the surface side.

When the positive electrode composition layer of the positive electrodeof the present invention is formed on only one side of the currentcollector, this positive electrode composition layer should satisfy thea/b value of 2 or more. When the positive electrode composition layer isformed on both sides of the current collector, each of these positiveelectrode composition layers should satisfy the a/b value of 2 or more.In either case, the a/b value is measured at three points, each beingapart from a same distance in the positive electrode composition layer.The average thereof should satisfy 2 or more.

When the elements derived from the binder are mapped by means of theSEM-EDX method on the cross-section of the positive electrodecomposition layer, the existence domains of the binder included in thepositive electrode composition layer can be shown, while the elementsderived from the other materials are shown at the same time. Forexample, consider a case where PVDF (i.e., polyvinylidene fluoride) isused as a binder. In this case, element C (carbon) detected in SEM-EDXis included most in the binder, but a mapping of which can show not onlythe binder but also the existence domains of the conductive assistant.When analyzing the positive electrode after the battery is disassembled,if mapping only the second most element, i.e., F (fluorine), included inthe binder, it may be possible to detect a film on the positiveelectrode formed by the fluorine-containing compound included in thenonaqueous electrolyte. In this way, selection of only one elementcannot always grasp the existence domains of the binder accurately.Therefore, among the elements detectable by SEM-EDX, each of the twoelements in the binder, i.e., the element most included in the binderand another element second most included in the binder, are each mapped.Thus, the accuracy of the judgment can be improved by identifying theportion where the element maps overlap with each other. In addition, inthis case, mapping of the elements derived from the electrolytes such P(phosphorus) or B (boron) can identify the residue from the electrolyte,not from the existence domains of the binder.

Next, the analysis method is explained.

The positive electrode in the electrode body is taken out, and thecross-section at the center in the longitudinal direction of thepositive electrode composition layer is the target for analysis. Thecross-section of the positive electrode is subject to an ion millingprocessing to expose the surface. With respect to the sample of thepositive electrode as provided, elements derived from the binder aredetected by means of SEM-EDX, and two kinds of the elements, i.e., theelement most included and another element second most included in thebinder are selected. An element mapping is carried out for each of thetwo elements, and the area (i.e., overlapping area) of the part wherethe element mappings of the two kinds overlap with each other iscalculated. Here, with respect to the total overlapping area of thecross-section of the positive electrode composition layer, a ratiopercentage, i.e., a %, is for the overlapping area of the domain Aextending from the central part to the surface side in the thicknessdirection, and a ratio percentage, i.e., b %, is for the overlappingarea of the domain B extending from the central part to the currentcollector side in the thickness direction. When the ratio a/b is 2 ormore, the folding strength of the positive electrode can be increased.It is preferable that the ratio a/b is 5 or more, and it is morepreferable that the ratio a/b is 10 or more. The ration a/b of theExamples and the Comparative Examples described later were obtained bythe method explained here.

The ratio a/b can be adjusted as follow. When forming a coating film byapplying a positive electrode composition on a current collector duringthe process of forming the positive electrode composition layer, thedrying step is carried out relatively at a low temperature at least atthe beginning stage of the drying, thereby adjusting it within the rangeas mentioned above. The detailed mechanism has not been yet clarified,but the following merits are considered. That is, the positive electrodeactive material (which will be described later) is included in thepositive electrode composition layer and has relatively a high specificgravity, and therefore, it can go down in the composition layer. Inother words, it can transfer to the side of the positive electrodecurrent collector. On the other hand, the binder has relatively a lowspecific gravity, and therefore, it can move to the surface side in thecomposition layer during the drying process. In addition, at a lowtemperature at least at the beginning stage of the drying, thephenomenon can be generated more significantly than drying at a hightemperature.

The specification condition of drying depends on the thickness of thepositive electrode composition layer, but it can be possible to adopt aset temperature of the dry means at 90 to 115° C. For example, the drymeans can include means to heat the coating film by a drying method byusing warm air through a dryer or by using a far infrared ray heater. Asthe dry means, a combination of plural dry methods can be used to heatand dry the coating film.

Also, after the coating film has dried at a low temperature at thebeginning of the dry process, then, it is preferable to raise thetemperature at relatively a high temperature of 120 to 150° C., therebyimproving the productivity of the positive electrode. In this case,plural dry means can be prepared such that the dry means at thebeginning stage of the dry process is set at 90 to 115° C., and the drymeans for the subsequent dry process is set at relatively a hightemperature of 120 to 150° C.

An example of the method for drying is explained in detail. First, apositive electrode composition is prepared, which is applied on onesurface of the positive electrode current collector, thereby forming acoating film. Then, it is transferred to a dry furnace to dry one sidethereof. At this time, several sets of dry means are prepared. Thetemperature of the first dry means (e.g., a dryer) located at the mostupstream in the dry furnace is set at 90 to 115° C., and the temperatureof the subsequent dry means (dryers) is set at 120 to 150° C. Then, thecurrent collector having formed the coating film of the positiveelectrode composition is transferred into the dry furnace. After dryingthe one side, a positive electrode composition is applied on the otherside of the positive electrode current collector to form a coating film,and the same method is carried out for drying. After finishing thedrying of the coating films of the positive electrode composition whichare applied on both sides of the positive electrode current collector, acalendar processing is carried out, if necessary. As a result, the ratioa/b can be adjusted to fall within the range of 2 or more. Theexplanation above regarding the method to adjust the ratio a/b is forthe purpose of showing an example only. So long as the positiveelectrode composition layer has the ratio a/b of 2 of more, the methodfor the drying is not specifically limited.

<Positive Electrode Active Material>

The positive electrode active material used for the positive electrodementioned above can use known active material such as lithium-containingtransition metal oxide, but which is not particularly limited thereto.For example, specific examples of the lithium-containing transitionmetal oxide can include Li_(x)CoO₂, Li_(x)NiO₂, Li_(x)MnO₂,Li_(x)Co_(y)Ni_(1-y)O₂, Li_(x)Co_(y)M_(1-y)O₂, Li_(x)Ni_(1-y)M_(y)O₂,Li_(x)Mn_(y)Ni_(z)Co_(1-y-z)O₂, Li_(x)Mn₂O₄, and Li_(x)Mn_(2-y)M_(y)O₄.In each of the structural formulae above, M is at least one metallicelement selected from the group consisting of Mg, Mn, Fe, Co, Ni, Cu,Zn, Al, Ti, Zr, Ge and Cr, and satisfy 0≤x≤1.1, 0≤y≤1.0, 1.0≤z≤2.0. Fromthe viewpoint of the energy density a layer-shaped compound includinglithium and cobalt (general formula LC_(1-y)M² _(y)O₂, where M² is thesame as M except for excluding Co, and y is the same as explainedbefore) is particularly preferable.

<Binder>

As the binder used for the positive electrode mentioned above, either athermoplastic resin or a thermosetting resin can be used, if it ischemically stable inside a battery. The example thereof can include onekind or two or more kinds of PVDF, polyethylene, polypropylene,polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP),vinylidene fluoride-hexafluoropropylene copolymer (P(VDF-HFP)), styrenebutadiene rubber (SBR), tetrafluoroethylene-hexafluoroethylenecopolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP),tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA),vinylidene fluoride-tetrafluoroethylene copolymer (P(VDF-TFE)),ethylene-tetrafluoroethylene copolymer (ETFE),polychlorotrifluoroethylene (PCTFE), propylene-tetrafluoroethylenecopolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer(P(VDF-CTFE)), ethylene-chlorotrifluoroethylene copolymer (ECTFE) orethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer,ethylene-acrylic acid methyl copolymer and ethylene-methyl methacrylatecopolymer, and Na ion crosslinkage form of those copolymers.

When mapping the elements derived from the binder after performing theSEM-EDX at the cross-section of the positive electrode as mentionedabove, and when selecting two elements, i.e., the element most includedand another element second most included in the binder, they areselected appropriately based on the kind of the binder as explainedabove.

When the binder used is a polymer including fluorine such as PVDF, PTFEand PCTFE, or a copolymer including these polymer, C (carbon) and F(fluorine) should be selected as the two elements.

<Conductive Assistant>

The conductive assistant used for the positive electrode mentioned aboveshould be one which is chemically stable in the battery. The examplesthereof can include: graphite such as natural graphite and artificialgraphite; carbon black such as acetylene black, ketjen black (brandname), channel black, furnace black, lampblack and thermal black;conductive fiber such as carbon fiber and metal fiber; metallic powdersuch as aluminium flakes; fluorocarbon; zinc oxide; conductive whiskersuch as potassium titanate; conductive metal oxide such as titaniumoxide; and organic conductive material such as polyphenylenederivatives; and these compounds can be used alone or in combination oftwo or more. Among these compounds, it is preferable to use graphitehaving a high conductivity, or carbon black having a superiorliquid-absorbing property. Also, the form of the conductive assistant isnot necessarily in a primary particle, but can be in aggregates such assecond aggregate or in an aggregates such as a chain structure. Theseaggregates are easy in handling and improves the productivity, as well.

<Current Collector>

The current collector used for the positive electrode mentioned abovecan be the same as conventionally used in the positive electrode ofknown nonaqueous electrolyte secondary batteries. For example, it ispreferable to use an aluminum foil having a thickness of 8 to 30 μm.

<Positive Electrode Composition Layer>

Regarding the positive electrode composition layer mentioned above, itis preferable that the total quantity of the positive electrode activematerial is 92 to 99 mass %, the quantity of the conductive assistant is0.5 to 6 mass %, and the quantity of the binder is 0.5 to 6 mass %. Itis favorable that the thickness of the positive electrode compositionlayer is 40 to 300 μm per one side of the current collector afterapplying a calendar processing.

The density of the positive electrode composition layer of the positiveelectrode of the present invention is 3.95 g/cm³ or more. In order toincrease the density of the positive electrode composition layer, two ormore kinds of positive electrode active material particles, each havingdifferent average particle diameter, are generally used. Then, thepositive electrode composition layer can become highly dense sincesmaller particles can be filled between larger particles.

In order to realize a positive electrode composition layer with a highdensity of 3.95 g/cm³ or more, the factors to be controlled can include:a particle size ratio between the particles of the positive electrodeactive material having the largest average particle diameter and theparticles of the positive electrode active material having the leastaverage particle diameter; each content thereof; and the content ratioof the particles of the positive electrode active material having thelargest average particle diameter and the particles of the positiveelectrode active material having the least average particle diameter inthe positive electrode active material.

It is noted that in the specification of the present application, theterm “the average particle diameter” of various particles means asfollow. A micro track particle size distribution measuring equipment,“HRA9320,” made by Nikkiso Co., Ltd. is used to measure a particle sizedistribution. Then, integral calculus volume is calculated from thesmaller particles thereof. In this case, the term corresponds to thevalue (d50) median diameter of the 50% diameter of the multiplicationfraction of the volume standard.

Also, the density of the composition layer in this specification meansthe value obtained by the measurement method below. A positive electrodehaving a predetermined area is cut out, and its weight is measured byusing an electronic balance having a minimum scale of 1 mg. This weightis subtracted by the weight of the current collector, thereby producingthe weight of the positive electrode composition layer. Also, the totalthicknesses of the positive electrode is measured at 10 points by usinga micrometer having a smallest scale of 1 μm. The thickness of thecurrent collector is subtracted from each total thickness as measuredabove, and their results are averaged. By using this average value andthe area, the volume of the positive electrode composition layer iscalculated. A density of the positive electrode composition layer can beobtained by dividing the weight of the positive electrode compositionlayer by the volume. The density of the composition layer of thenegative electrode can be obtained in the same manner.

In order to make the positive electrode composition layer have a densityof 3.95 g/cm³ or more, the following means can be adopted, for example.

<Option 1>

It is preferable that positive electrode active material particleshaving an average particle diameter of 1-10 μm (i.e., positive electrodeactive material particles having a smaller average particle diameter)are mixed with positive electrode active material particles having anaverage particle diameter of 20-30 μm (i.e., positive electrode activematerial particles having a larger average particle diameter). That is,particles of the positive electrode active materials with two differentaverage particle diameters are preferably mixed. By using large andsmall particles of the positive electrode active materials, the smallparticles can fill in the gap made between the large particles, therebyincreasing the density of the positive electrode composition layer.

<Option 2>

Two kinds of positive electrode active material particles having twodifferent average particle diameters are combined. Assume that theaverage particle diameter of the positive electrode active materialparticle having a small average particle diameter is ds (μm). Assumealso that the average particle diameter of the positive electrode activematerial particle having a large average particle diameter is dl (μm).Then, it is preferable that a ratio dl/ds is 3 to 15. When the averageparticle diameters of the two kinds of the positive electrode activematerial particles have the relationship above, the small particles caneasily fill in the gap made between the large particles, therebyincreasing the density of the positive electrode composition layer.

<Option 3>

Two kinds of positive electrode active material particles having twodifferent average particle diameters are combined. It is preferable thatthe positive electrode active material particle having a small averageparticle diameter and the positive electrode active material particlehaving a large average particle diameter are mixed at a mixture ratio of40:60 to 60:40. By adopting the mixture ratio above, it is possible toobtain such a quantity ratio that the small particles can just fill inthe gap made between the large particles, thereby increasing the densityof the positive electrode composition layer.

Several means are described above, but a combination of plural means asexplained above can further increase the density of the positiveelectrode composition layer. It is possible that the density of thepositive electrode composition layer can be particularly increased byemploying all three means above. In addition, it is preferable that thedensity of the positive electrode composition layer can be 5.0 g/cm³ orless in view of feasibility.

[Negative Electrode]

The negative electrode used in the nonaqueous electrolyte secondarybattery of the present invention can be provided with, for example, astructure having a negative electrode composition layer including anegative electrode active material and a binder, and a conductiveassistant if necessary formed on one side of both sides of a currentcollector.

<Negative Electrode Active Material>

As the negative electrode active material mentioned above, there is nospecific limitation, and any material which has been conventionally usedin known nonaqueous electrolyte secondary batteries can be used, if itcan store and release lithium ions. The examples thereof can includegraphite, thermolysis carbon, coke, glassy carbon, burned form oforganic high molecular compound, mesocarbon microbeadses (MCMB), andcarbon fiber. These compounds are carbon based materials which can storeand release lithium ions. These compounds can be used alone or incombination of two kinds or more to form a negative electrode activematerial. In addition, other examples which can be used as a negativeelectrode active material can include elements such as silicon (Si), tin(Sn), germanium (Ge), bismuth (Bi), antimonial (Sb) and indium (In), andtheir alloys; a compound close to lithium metal that can be charged ordischarged at a low voltage such as lithium-containing nitride orlithium-containing oxide; and lithium metal or lithium/aluminum alloy.Among them, material represented by SiO_(x), that includes silicon andoxygen as constituent elements, can be preferably used as a negativeelectrode active material.

The SiO_(x) can include microcrystals or an amorphous phase of Si. Inthis case, the atomic ratio of Si and O is determined with including themicrocrystals or the amorphous phase of Si. In other words, the SiO_(x)can be provided in a structure in which Si (e.g., microcrystalline Si)is dispersed in an amorphous SiO₂ matrix, where the atomic ratio x canbe determined by including the amorphous SiO₂ and the Si dispersed inthe amorphous SiO₂, satisfying 0.5≤x≤1.5. For example, when the materialis provided as having a structure in which Si is dispersed in anamorphous SiO₂ matrix, and the molar ratio of SiO₂ and Si is 1:1, thestructural formula of this material can be represented by SiO becausex=1 is established. In the case of the material having such a structure,a peak due to the presence of Si (microcrystalline Si) might not beobserved, e.g., by X-ray diffraction analysis, but the presence of fineSi can be confirmed by transmission electron microscope observation.

Also, it is favorable that SiO_(x) as explained above is a complex witha carbon material, and for example, it is desirable that the surface ofSiO_(x) is coated with a carbon material. Usually, SiO_(x) has a poorconductivity. Therefore, if this is used as a negative electrode activematerial, in view of securing good battery properties, a conductivematerial (i.e., conductive assistant) is used, such that the mixing anddispersing of the SiO_(x) and the conductive material in the negativeelectrode are made better, thereby forming a superior conductivenetwork. By using such a complex of SiO_(x) and carbon material, abetter conductive network can be formed in the negative electrode ratherthan using a material obtained by merely mixing SiO_(x) with carbonmaterial.

<Binder>

As the binder mentioned above, the examples thereof can include starch,polyvinyl alcohol, polyacrylic acid, carboxymethylcellulose (CMC),hydroxypropyl cellulose, regenerated cellulose and polysaccharides suchas diacetyl cellulose, and denatured form thereof; thermoplastic resinssuch as polyvinyl chloride, polyvinylpyrrolidone (PVP),polytetrafluoroethylene, polyvinylidene fluoride, polyethylene,polypropylene, polyamideimide and polyamides, and denatured formthereof; polyimide; and polymers having a rubber elasticity such asethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrenebutadiene rubber (SBR), butadiene rubber, polybutadiene, fluorinepolymer and polyethylene oxide and denatured form thereof. Thesecompounds can be used alone or in combination of two or more.

<Conductive Assistant>

The negative electrode composition layer as mentioned above can furtherinclude a conductive material as a conductive assistant. Such aconductive material is not particularly limited so long as it does notcause a chemical reaction inside the battery. The examples can includecarbon black (e.g., thermal black, furnace black, channel black, ketjenblack, acetylene black), carbon fibers, metal powders (e.g., powders ofe.g., copper, nickel, aluminum, silver and etc.), metal fibers,polyphenylene derivatives (ones disclosed in Japanese Laid-Open PatentPublication No. S59-20971). These compounds can be used alone or incombination of two or more kinds. Of these examples, it is preferable touse carbon black, and ketjen black and acetylene black are morepreferable.

<Current Collector>

As the current collector, the examples there can include a foil, punchedmetal, mesh or expanded metal, made of copper or nickel. Generally, acopper foil can be used. When this negative electrode current collectoris configured to reduce the thickness of the whole negative electrode inorder to obtain a battery of a high energy density, it is preferablethat the upper limit of the thickness is 30 μm. It is also desirablethat the lower limit is 5 μm in view of securing a mechanical strength.

<Manufacturing Method of the Negative Electrode>

The example of a method for manufacturing a negative electrode isexplained here. A negative electrode active material and a binder, and aconductive assistant if necessary are dispersed into a solvent such asNMP or water to prepare a paste or slurry form of a compositioncontaining a negative electrode composition, which is then applied toone surface or both surfaces of a current collector. After drying, acalendar process is applied if necessary, so as to prepare a negativeelectrode. However, the manufacturing method of a negative electrode isnot limited thereto, and another method can be adopted to prepare it.

<Negative Electrode Composition Layer>

Regarding the negative electrode composition layer mentioned above, itis preferable that the total quantity of the negative electrode activematerial is 80 to 99 mass % and the quantity of the binder is 1 to 20mass %. Also, when conductive material is used as a conductive assistantadditionally, the conductive material in the negative electrodecomposition layer can be added to the extent that the total quantitiesof the negative electrode active material and the quantity of the bindersatisfy the preferable ranges of these contents above. For example, thethickness of the negative electrode composition layer is preferably 40to 400 μm in consideration of the thickness of the positive electrodecomposition layer as mentioned before.

<Electrode Body>

The positive electrode of the invention is used in a nonaqueouselectrolyte secondary battery including an electrode body comprising apositive electrode, a negative electrode and a separator, and anonaqueous electrolyte, where is housed inside an exterior body. Inaddition, the electrode body includes at least one folded portion at thepositive electrode. Here, the folded portion refers to a point folded ora point where the curvature there is extremely small (for example, ithas a radius of curvature of 2 mm or less). The examples of an electrodebody having a positive electrode including such a folded portion are asfollows: one example is a winding electrode body (i.e., flat-shapedwinding electrode body) in which a positive electrode, a negativeelectrode and a separator, each being in strip shape, are stacked witheach other and wound in an eddy form such that its cross-section is madeinto a flat shape; and another example is an electrode body in which apositive electrode, a negative electrode and a separator are wound intoan eddy form such that it is housed inside a cylindrical exterior havinga diameter of 3.5 mm or less.

When the electrode body is provided with an adhesive layer either orboth between the positive electrode and the separator, or/and betweenthe negative electrode and the separator, it is easy to give the effectsof the present invention. When such an adhesive layer is included, theelectrode body is prepared by unifying the separator with the electrodethrough a process (i.e., press process) to press to have the electrodeadhere to the separator. Using a nonaqueous electrolyte secondarybattery using the electrode body with the electrode unified with theseparator, there can be expected to give an effect that the change inthe shape of the electrode body is restrained even if repeating chargeand discharge. Particularly in case of the flat-shaped winding electrodebody as explained above, it is remarkable to obtain such an effect.

In that case, in order to make a positive electrode composition layerhaving a very high density of 3.95 g/cm³ or more, the positive electrodemust have been applied to a more severe situation when pressing.However, in this way the positive electrode of the present invention canbe provided with a high tensile strength to endure such a severecondition.

In order to provide an adhesive layer either or both between thepositive electrode and the separator, or/and between the negativeelectrode and the separator, the exemplified form can be as follows: Anadhesive layer is provided on one side of the separator; an adhesivelayer is provided on both sides of the separator; an adhesive layer isprovided on both sides of the negative electrode; an adhesive layer isprovided at the negative electrode side of the separator, and isprovided on both sides of the positive electrode; and etc. Inparticularly, it is preferable that when providing an adhesive layer onboth sides of the separator, it becomes easy to produce batteries.

It is preferable to include an adhesive layer including an adhesiveresin (C) whose adhesive property can be developed by heating. In caseof adhesive layer including an adhesive resin (C), the electrode can beunified with the separator through a process (hot-press) to press theelectrode while heating. The lowest temperature to develop the adhesiveproperty of the adhesive resin (C) is required to be lower than thetemperature to start the shut-down in the other layers of the separatorthan the adhesive layer. In particular, it is preferably 60° C. or more,and 120° C. or less. Also, if the other layers of the separator than theadhesive layer include a resin porous layer (I) and a heat resistanceporous layer (II) as discussed later, the lowest temperature to developthe adhesive property of the adhesive resin (C) is required to be lowerthan the melting point of the resin (A), that is, the main components ofthe resin porous layer (I) (whose details will be discussed later).

By using such an adhesive resin (C), when applying the hot-press to theseparator and the positive electrode and/or the negative electrode to beunified, it is possible to restrict the deterioration of the separator.

By the existence of the adhesive resin (C), there can be the followingpeel strength between the separator and the electrode constitutingelectrode body (e.g., negative electrode) if carrying out a peel test at180°. In a condition before hot-press, it is preferably 0.05N/20 mm orless, and particularly preferably ON/20 mm (a state where no adhesivestrength exists). In a condition after applying hot-press at atemperature of 60 to 120° C., it is preferable to show a delayed tackcharacteristic of 0.2N/20 mm or more.

However, when the peel strength is too strong, the electrode compositionlayers (i.e., the positive electrode composition layer and the negativeelectrode composition layer) can be peeled from the current collector ofthe electrode, and thereby the conductivity might be decreased.Therefore, the peel strength at the peel test at 180° is preferably10N/20 mm or less in a condition after having applied hot-press at atemperature of 60 to 120° C.

In addition, in this specification, the peel strength at 180° between anelectrode and a separator can be the value measured in accordance withmethod below. Each of a separator and an electrode is cut to have a sizeof 5 cm in length and 2 cm in width. Thereby obtained cut separator isstacked on the electrode cut. When measuring the peel strength of thecondition after hot press, the area of 2 cm×2 cm from one end thereof issubject to hot press to prepare a test sample. With respect to the testsample, the separator and the electrode are opened at the other endwhere the hot press is not applied, and the separator and the negativeelectrode are bent to create an angle of 180° therebetween. Then, usinga tensile strength test equipment, the test sample is held by theequipment such that the one end of the separator and the other end ofthe electrode, these ends making the angle of 180°. The test sample ispulled at a speed of 10 mm/min to measure the strength when thehot-pressed domain of the separator and the electrode is peeledtherefrom. Also, the peel strength of the test sample in a conditionbefore hot press the separator and the electrode can be measured in thesame manner as explained above, except for the following difference.That is, the cut separator is stacked on the electrode cut as explainedabove, but then, the press is applied without heating to prepare a testsample.

Therefore, it is preferable that the adhesive resin (C) has littleadhesive property (i.e., adhesiveness) at room temperature (e.g., 25°C.) and has a delayed tack property such that the minimum temperature todevelop the adhesive property is lower than the temperature that theseparator shuts down, preferably e.g., 60° C. or more and 120° C. orless. In addition, it is more preferable that the temperature to applythe hot press unify a separator with an electrode is 80° C. or more and100° C. or less so that the thermal contraction of the separator doesnot significantly produce. It is also preferable that the minimumtemperature where the adhesive property of the adhesive property resin(C) develops is 80° C. or more and 100° C. or less.

The adhesive resin (C) having a delayed tack property can be preferablya resin having characteristics in which it has little fluidity at roomtemperature but shows a fluidity when heat it to adhere by pressing.Also, the adhesive resin (C) can be one that is solid at roomtemperature but melts when heating it so as to develop an adhesiveproperty through a chemical reaction.

It is preferable that the adhesive resin (C) has a softening point, thatis an index such as melting temperature and glass transitiontemperature, within a range of 60° C. or more and 120° C. or less. Forexample, the melting temperature of the adhesive resin (C) can bemeasured in accordance with the method defined in JIS K 7121, and theglass transition temperature of the adhesive resin (C) can be measuredin accordance with the method defined in JIS K 7206.

The specific examples of such an adhesive resin (C) can include lowdensity polyethylene (LDPE), poly-α-olefin (for example, polypropylene(PP) and polybutene-1), polyacrylate, ethylene-vinyl acetate copolymer(EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylatecopolymer (EEA), ethylene-butyl acrylate copolymer (EBA),ethylene-methyl methacrylate copolymer (EMMA), and an ionomer resin.

In addition, the adhesive resin (C) used can be provided with a coreshell structure in which the core includes a various kind of resins or aresin having an adhesiveness at room temperature such as SBR, nitrilerubber (NBR), fluorine rubber and ethylene-propylene rubber, and theshell includes a resin whose melting temperature or softening point isin a range of 60° C. or more and 120° C. or less. In this case, theshell used can be of e.g., an acrylic resin or polyurethane.Furthermore, the adhesive resin (C) used can be one package type ofpolyurethane or epoxy resin, showing an adhesive property in the rangeof 60° C. or more and 120° C. or less.

The resin used in the adhesive resin (C) can be alone or in combinationof two or more kinds.

The commercial products of the adhesive resin (C) having a delayed tackproperty as explained above can include “MORESCO-MELT EXCEL PEEL”(polyethylene, brand name) made by Matsumura Oil Research Co. Ltd.,“AQUATEX” (EVA, a brand name) made by Co., Ltd., EVA made by NipponUnicar Cororation, “HEAT MAGIC” (EVA, a brand name) made by Toyo InkCo., Ltd., “EVAFLEX-EEA Series” (ethylene-acrylic acid copolymer, brandname) made by Du Pont-Mitsui Polychemical Co., Ltd., “ARONTACK TT-1214”(acrylic ester, brand name) made by Toagosei Co., Ltd., and “HIMILAN”(ethylene type ionomer resin, brand name) made by Du Pont-MitsuiPolychemical Co., Ltd. Corporation.

In addition, when an adhesive layer is formed such that substantially nocavities are formed by the adhesive resin (C), the nonaqueouselectrolyte of the battery might be difficult to come into contact withthe surface of the electrode including a unified separator. Therefore,on the surfaces existing the adhesive resin (C) of the positiveelectrode, the negative electrode and the separator, it is preferablethat a domain where the adhesive resin (C) exists is formed whileforming another domain where it does not. In details, the domain wherethe adhesive resin (C) exists and the other domain where it does not canbe formed in strip form in turn. Or, the adhesive resin (C) can beformed in a discontinuous manner in plural existence domains, e.g., wheneach domain is in a shape of circle in the plan view. In these cases,the existence domains of the adhesive resin (C) can be located regularlyor at random.

On the surfaces existing the adhesive resin (C) of the positiveelectrode, the negative electrode and the separator, it is preferable toform a domain where the adhesive resin (C) exists while forming anotherdomain where it does not. For example, the area (total area) of thedomain where the adhesive resin (C) exists can be adjusted such that thepeel strength at 180° after heat press of the separator and theelectrode falls within the range as explained before. It can fluctuatedepending on the kind of the adhesive resin (C) to be used, but indetails, it is preferable that the adhesive resin (C) exists at 10 to60% of the area of the surface where the adhesive property resin (C)exists.

In addition, on the surface where the adhesive property resin (C)exists, it is preferable to consider the targeted application weight ofthe adhesive resin (C) in order to obtain favorable adhesion with theelectrode as well as to adjust the peel strength at 180° after hot pressof the separator and the electrode within the range as explained before.That is, it is preferably 0.05 g/m² or more and more preferably 0.1 g/m²or more. However, on the surface where the adhesive property resin (C)exists, if the targeted application weight of the adhesive resin (C) istoo much, the thickness of the electrode body might be excessivelyincreased, or the adhesive resin (C) might block the cavities of theseparator to interrupt the migration of ions in the battery. Thus, onthe surface where the adhesive property resin (C) exists, it ispreferable that the targeted application weight of the adhesive resin(C) is 1 g/m² or less, and more preferably 0.5 g/m² or less.

[Separator]

In the nonaqueous electrolyte secondary battery using the positiveelectrode of the present invention, it is possible to use a film-formedseparator primarily made of polyolefin such as polyethylene, or a knownseparator of nonwoven fabric.

In particular, it is preferably to use a separator including a resinporous layer (I) primarily made of a resin (A) having a meltingtemperature of 100 to 170° C., and a heat resistance porous layer (II)primarily made of fillers (B) having a heat-resistant temperature of150° C. or more and therefore, the heat resistance porous layer (II)does not melt at a temperature of 150° C. or less. In this way, it ispossible to prevent the separator from thermal contraction at a hightemperature. The resin porous layer (I) is a layer serving as originalseparator function to prevent short circuit between the positiveelectrode and the negative electrode while allowing ions to passtherethrough. The heat resistance porous layer (II) is a layer to play arole to give heat resistance to the separator.

The resin porous layer (I) has a melting temperature of 100° C. or moreand 170° C. or less. Namely, the resin porous layer (I) is mainlycomposed of a resin (A) having a melting temperature of 100° C. or moreand 170° C. or less, when it is measured by means of a differentialscanning calorimeter (DSC) in accordance with JIS K 7121. By using aseparator having the resin porous layer (I) mainly composed of the resin(A), so-called shut-down function can be given such that the pores ofthe separator are blocked by molten thermoplastic resin when thetemperature inside the battery becomes high.

The resin (A) as a main component of the resin porous layer (I) is notparticularly limited, but it should have the features below; it has amelting temperature of 100° C. or more and 170° C. or less; it has anelectrically insulating property; it is electrochemically stable; and itis stable to the nonaqueous electrolyte and the medium used in thecomposition for making the heat resistance porous layer (II) asdiscussed later; and it is a thermoplastic resin. Preferable examplesthereof can include polyolefin such as polyethylene (PE), polypropylene(PP) and ethylene-propylene copolymer.

The resin porous layer (I) can include, for example, a polyolefin fineporous membrane conventionally used in nonaqueous electrolyte secondarybatteries such as lithium secondary batteries. That is, it can have astructure in which a film or sheet of a polyolefin having mixed withinorganic fillers is subject to uniaxial or biaxial stretching so as toform fine pores. Or, the resin porous layer (I) can be provided with astructure in which a mixture of the resin (A) and another resin is madeinto a film or sheet, which is then immersed in a solvent that candissolve only said another resin, thereby forming pores by dissolvingsaid another resin.

In addition, the resin porous layer (I) can include fillers for thepurpose of improving the strength. For example, the fillers used herecan the same as the examples of the fillers (B) used in the heatresistance porous layer (II) as described later.

In this specification, the phrase “mainly composed of a resin (A)” inthe resin porous layer (I) means a condition where the resin (A) isincluded at 70 volume % or more in the total volume of the components ofthe resin porous layer (I). The quantity of the resin (A) in the resinporous layer (I) is preferably 80 volume % or more, and more preferably90 volume % or more in the total volume of the components of the resinporous layer (I).

The heat resistance porous layer (II) is mainly composed of a resinwhich does not melt at temperature of 150° C. or less, or fillers (B)having a heat-resistant temperature of 150° C. or more.

When the heat resistance porous layer (II) includes a resin having amelting temperature of 150° C. or more, for example, one embodiment canbe a structure in which a fine porous membrane made of a resin whichdoes not melt at temperature of 150° C. or less (e.g., fine porousmembrane for batteries made of PP as explained before) is laminated onthe resin porous layer (I). Another embodiment can be a structure inwhich a dispersion liquid including particles of resin which does notmelt at temperature of 150° C. or less is applied on the porous layer(I) and dried, thereby forming a porous layer (II) on the surface of theporous layer (I).

The examples of the resin which does not melt at a temperature of 150°C. or less can include: PP; fine particles of various crosslinkedpolymer such as crosslinked polymethyl methacrylate, crosslinkedpolystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzenecopolymer crosslinkage product, polyimide, melamine resin, phenolicresin, and benzoguanamine-formaldehyde condensate; polysulfone;polyethersulfone; polyphenylene sulfide; polytetrafluoroethylene;polyacrylonitrile; aramid; and polyacetal.

When using particles of the resin which does not melt at a temperatureof 150° C. or less, Regarding the particle size of the particles, theaverage particle diameter is preferably, for example, 0.01 μm or more,and more preferably 0.1 μm or more, but it is 10 μm or less, and morepreferably 2 μm or less.

When the heat resistance porous layer (II) includes fillers (B) having aheat-resistant temperature of 150° C. or more, there is no particularlimitation if the fillers (B) have a heat-resistant temperature of 150°C. or more, are electrochemically stable in the battery and stable tothe nonaqueous electrolyte in the battery. Regarding the fillers (B) inthe instant specification, the phrase “having a heat-resistanttemperature of 150° C. or more” refers to a condition where there is novisible change in the shape, such as deformation, at a temperature of atleast 150° C. The heat-resistant temperature of the filler (B) ispreferably 200° C. or more, and more preferably 300° C. or more, and yetmore preferably 500° C. or more.

It is preferable that the fillers (B) are inorganic fine particle havingelectrically insulating property. Specifically, the examples thereof caninclude: inorganic oxide fine particles such as iron oxide, silica(SiO₂), alumina (Al₂O₃), TiO₂ and BaTiO₃; inorganic nitride fineparticles such as aluminum nitride and silicon nitride; insoluble ioniccrystal fine particles such as calcium fluoride, barium fluoride andbarium sulfate; covalent crystal fine particles such as silicon anddiamond; clay fine particles such as montmorillonite; and etc. Here, theinorganic oxide fine particles can be material derived from mineralresources or material artificially made, including boehmite, zeolite,apatite, kaolin, mullite, spinel, olivine and mica. Also, the inorganiccompound constituting the inorganic fine particles can be one havingapplied a process for element substitution or solid solution, ifnecessary and it is also possible to apply a surface treatment to theinorganic fine particles. Also, the inorganic fine particles can be aconductive material including conductive oxide such as metal, SnO₂ andtin-indium oxide (ITO), and carbonaceous material such as carbon blackand graphite, the surfaces of which can be covered with a materialhaving an electrically insulating property (e.g., inorganic oxides),thereby giving an electrically insulating property.

The filler (B) used can be fine organic particles. The specific examplesof the fine organic particles can include: fine particles of crosslinkedpolymer such as polyimide, melamine type resin, phenolic type resin,crosslinked polymethylmethacrylate (crosslinked PMMA), crosslinkedpolystyrene (crosslinked PS), polydivinylbenzene (PDVB), andbenzoguanamine-formaldehyde condensate; fine particles of heatresistance polymer such as thermoplastic polyimide; and etc. The organicresin (polymer) constituting the fine organic particles can be amixture, denatured form, derivative, copolymer (random copolymer,alternating copolymer, block copolymer, graft copolymer) or crosslinkedform (in the case of the heat resistance polymer explained before) ofthe material exemplified above.

The fillers (B) used can be of one kind, or two kinds or more incombination, of the material exemplified above. Among the fillersexemplified above, it is preferable to use inorganic oxide fineparticles. In particular, it is preferable to use at least one kindselected from the group consisting of alumina, silica and boehmite.

The average particle diameter of the fillers (B) is preferably 0.001 μmor more, and more preferably 0.1 μm or more, and is preferably 15 μm orless, and more preferably 1 μm or less.

The shape of the filler (B) can be, for example, a shape near aspherical shape, or a plate-shape. In view of the short circuitprevention, it is preferable to be a plate-shape. The representativeexample of such a plate-shaped particles can include plate-shaped Al₂O₃or plate-shaped boehmite.

In addition, when the nonaqueous electrolyte secondary battery using theresin porous layer (I) and the heat resistance porous layer (II) isrequired to show a high output performance, it is preferable to usefillers (B) having a secondary particle structure in which a primaryparticle aggregates. By using tuft-formed fillers, the cavities of theheat resistance porous layer (II) can be enlarged, thereby producing abattery with a high output performance.

In this specification, the phrase “mainly composed of” with respect tothe heat resistance porous layer (II) means a condition where one isincluded at 70 volume % or more in the total volume of the components ofthe resin porous layer (II). The quantity of the fillers (B) in the heatresistance porous layer (II) is preferably 80 volume % or more, and morepreferably 90 volume % or more in the total volume of the components ofthe heat resistance porous layer (II). When the fillers (B) are includedin the heat resistance porous layer (II) at a high content as explainedabove, thermal contraction of the separator as a whole can be favorablycontrolled, thereby giving high heat resistance.

In addition, it is preferable that the heat resistance porous layer (II)includes an organic binder in order to adhere to the fillers (B) eachother, or between the heat resistance porous layer (II) and the resinporous layer (I). From the view point above, the upper limit of thequantity of the fillers (B) in the heat resistance porous layer (II) issuitably 99 volume % in total volume of the components of the heatresistance porous layer (II). Also, when the quantity of the fillers (B)in the heat resistance porous layer (II) is less than 70 volume %, forexample, it is necessary to increase the quantity of the organic binderof in the heat resistance porous layer (II). In that case, the pores ofthe heat resistance porous layer (II) can be filled with the organicbinder, and therefore, the function of the separator might be loss.

The organic binder used for the heat resistance porous layer (II) is notparticularly limited, if it can favorably adhere to fillers (B) eachother as well as between the heat resistance porous layer (II) and theresin porous layer (I), and if it is electrochemically stable, and if itis stable to the nonaqueous electrolyte liquid for the electrochemicalelements. The examples thereof can include fluoric resin [e.g.,polyvinylidene fluoride (PVDF)], fluorine type rubber, SBR,carboxymethylcellulose (CMC), hydroxyethyl cellulose (HEC), polyvinylalcohol (PVA), polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP),poly-N-vinyl acetamide, crosslinked acrylic resin, polyurethane andepoxy resin. The organic binder used can be one kind, or two or morekinds in combination.

In addition, when using the organic binder, it can be used in anembodiment in which the organic binder is dissolved in a medium of thecomposition (e.g., slurry) for making the heat resistance porous layer(II), or dispersed as an emulsion state, as described later.

The cavity rate of the heat resistance porous layer (II) can beconsidered as follow. In order to secure the retention quantity of thenonaqueous electrolyte of the nonaqueous electrolyte secondary batteryand favorably accomplish ion permeability, the cavity rate is preferably40% or more, and more favorably 50% or more, at a dry condition. On theother hand, from the viewpoint to secure the strength and prevent theinternal short circuit, it is preferable that the cavity rate of theheat resistance porous layer (II) is 80% or less, and more preferably70% or less.

The separator can include one layer of the resin porous layer (I) andone layer of the heat resistance porous layer (II), or plurality layersof them. In details, only one surface of the resin porous layer (I) canbe provided with the heat resistance porous layer (II) to form aseparator. Or, both surfaces of the resin porous layer (I) can beprovided with the porous layer (II) to form a separator. However, if thenumber of the layers to constitute the separator is increased, thethickness of the separator will increase, and therefore, the internalresistance of the electrochemical element might increase or the energydensity might fall to bring about unfavorable results. Thus, the numberof the layers in the separator is preferably five layers or less.

The example of the method for preparing the separator of the presentinvention is explained. For example, a composition for forming aheat-resistant porous layer (II) including fillers (B) (e.g., a liquidcomposition such as slurry) is applied on a resin porous layer (I), anddry it at a predetermined temperature. Then, a solution or emulsionincluding an adhesive resin (C) is applied thereon, and dried it at apredetermined temperature. Thereby, such an adhesive resin (C) can beformed on a separator including the resin porous layer (I) and the heatresistance porous layer (II).

In addition to the filler (B), the heat-resistant composition forforming the porous layer (II) includes an organic binder and etc., whichare dispersed in a solvent (which can be a disperse medium, and the samenotion is applied hereinafter.). It is noted that the organic binder canbe dissolved in a solvent. The solvent used for a composition forforming the heat-resistant porous layer (II) is not particularlylimited, if it can disperse fillers (B) and etc. uniformly therein andcan dissolve or disperse an organic binder uniformly. The examplesthereof can be general organic solvents including aromatic hydrocarbonssuch as toluene, furans such as tetrahydrofuran, the ketones such asmethyl ethyl ketone and methyl isobutyl ketone. It is noted that for thepurpose of controlling the surface tension, the solvent can include anadditive such as alcohol (e.g., ethylene glycol, propylene glycol), andvarious propylene oxide type glycol ether such as or monomethyl acetate.When the organic binder is water-soluble, water can be used as a solventto form an emulsion, but in this case, an alcohol (methyl alcohol, ethylalcohol, isopropyl alcohol, ethylene glycol) can be appropriately addedto control surface tension.

It is preferable that the composition for forming the heat resistantporous layer (II) includes 10 to 80 mass % of a solid content includingthe filler (B) and the organic binder.

A stacked product of the resin porous layer (I) and the heat-resistantporous layer (II) can be obtained as explained above, onto which asolution or emulsion including the adhesive property resin (C) isapplied to form an adhesive layer, thereby producing a separator. It isnoted that in this case, the heat-resistant porous layer (II) can beformed on one surface or both surfaces of the resin porous layer (I),and that the adhesive property resin (C) can be provided on one surfaceor both surfaces of the stacked product of the resin porous layer (I)and the heat-resistant porous layer (II).

In particular, it is preferable that the first adhesive layer, the resinporous layer (I), the heat-resistant porous layer (II) and the secondadhesive layer are stacked in this order. In this configuration, theadhesive layer is located at the both sides of the negative electrodeand the positive electrode, so that an electrode body, especially aflat-shaped winding electrode body, can further restrain the change inshape due to the charge and discharge, thereby maintaining the originalthickness.

Also, in order to more effectively give the effects from theconstituting components such as fillers (B), it is possible to adopt anembodiment in which the constituting components are located at an unevendistribution such that the constituting components gather in a domain oflayer parallel or almost parallel to the film surface of the separator.

However, the method to prepare a separator is not limited thereto, andit can be prepared in accordance with another method. For example, thecomposition for forming the heat resistant porous layer (II) asexplained above can be applied on a surface of a substrate such as aliner, followed by drying to form a heat-resistant porous layer (II),which is then removed from the substrate. Then, the heat-resistantporous layers (II) is laminated on a fine porous film to become a resinporous layer (I), and a heat press is applied to unify them, therebyobtaining a stacked product. Then, an adhesive resin (C) is formed onone surface or both surfaces of the stacked product in the same manneras explained before, so as to obtain a separator.

The thickness of the separator produced in this way is preferably 6 μmor more, and more preferably 10 μm or more, in view of surely separatingthe positive electrode from the negative electrode. On the other hand,when the separator becomes too thick, the energy density of the batterymight decrease. Therefore, it is preferable that the thickness is 50 μmor less, and more preferably 30 μm or less.

Furthermore, the thickness of the resin porous layer (I) (Note that if aplural layers of the resin porous layer (I) exist, it should be a totalthickness.) is preferably 5 μm or more, but preferably 30 μm or less.Also, the thickness of the heat-resistant porous layer (II) (Note thatif a plural layers of the heat-resistant porous layer (II) exist, itshould be a total thickness.) is preferably 1 μm or more, and morepreferably 2 μm or more, and yet more preferably 4 μm or more, butpreferably 20 μm or less, and more preferably 10 μm or less, and yetmore preferably 6 μm or less. When the resin porous layer (I) is toothin, the shut-down performance might become weak. When it is too thick,the energy density of the battery might decrease, and in addition, thepower to bring about thermal contraction might increase too much solarge that the effects to control the thermal contraction of theseparator as a whole become insufficient. Also, when the heat-resistantporous layer (II) is too thin, the effects to control the thermalcontraction of the separator as a whole might become insufficient.However, when it is too thick, the thickness of the separator as a wholemight increase.

The cavity rate of the separator as a whole can be considered as follow.In order to secure the retention quantity of the nonaqueous electrolyteliquid of the nonaqueous electrolyte secondary battery and favorablyaccomplish ion permeability, the cavity rate is preferably 30% or moreat a dry condition. On the other hand, from the viewpoint to secure thestrength of the separator and prevent the internal short circuit, thecavity rate of the separator is preferably 70% or less at a drycondition.

The separator desirably has a Gurley value of 30 to 300 sec. The Gurleyvalue is obtained by a method according to JIS P 8117 and expressed asthe duration of the second it takes for 100 ml air to pass through amembrane at a pressure of 0.879 g/mm². If the air permeability is toolarge, the ion permeability may deteriorate. On the other hand, if theair permeability is too small, the strength of the separator maydecline.

A nonaqueous electrolyte secondary battery using the positive electrodeof the present invention can be prepared by using the electrode below.The positive electrode and the negative electrode as explained beforeare stacked with each other with intervention of a separator, which arethen wounded in eddy form, and pressed to be shaped into thecross-section flat. Then, a heat press process is applied to obtain aflat-shaped winding electrode body. Then, the electrode, e.g., theflat-shaped winding electrode body as explained above, is housed insidean exterior body along with a nonaqueous electrolyte. As a result, anonaqueous electrolyte secondary battery of the present invention can beobtained.

[Nonaqueous Electrolyte]

The nonaqueous electrolyte used can be a solution (i.e., nonaqueouselectrolyte liquid) which has been prepared by dissolving a lithium saltin the following nonaqueous solvent.

The examples of the solvent can include aprotic organic solvents such asethylene carbonate (EC), propylene carbonate (PC), butylene carbonate(BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methylethylcarbonate (MEC), γ-butyrolactone (γ-BL), 1,2-dimethoxyethane (DME),tetrahydrofuran (THF), 2-methyltetrahydrofuran, dimethyl sulfoxide(DMSO), 1,3-dioxolane, formamide, dimethylformamide (DMF), dioxolane,acetonitrile, nitromethane, methyl formate, methyl acetate, phosphatetriester, trimethoxy methane, dioxolane derivative, sulfolane,3-methyl-2-oxazolidinone, propylene carbonate derivative,tetrahydrofuran derivative, diethyl ether, and 1,3-propane sultone. Thecompound used can be one kind, or a mixture of two or more kinds.

The examples of the lithium salt contained in the nonaqueous electrolyteliquid can include lithium salts such as LiCO₄, LPF₆, LiBF₄, LiAsF₆,LiSbF₆, LiCF₃SO₃, LiCF₃CO₂, Li₂C₂F₄(SO₃)₂, LiN(CF₃SO₂)₂, LiC(CF₃SO₂)₃,LiC_(n)F_(2n+1)SO₃ (n≥₂) and LiN(RfOSO₂)₂ (where Rf represents afluoroalkyl group). The concentration of the lithium salt in thenon-aqueous electrolytic solution is preferably 0.6 to 1.8 mol/L, andmore preferably 0.9 to 1.6 mol/L.

In addition, the nonaqueous electrolyte used in the nonaqueouselectrolyte secondary battery can further contain additives in view offurther improvement of the charge discharge cycle characteristics or forthe purpose to improve the safety features such as high temperaturestorage property and overcharge prevention property. The examples of theadditives that can be appropriately added can include vinylenecarbonate, vinylethylene carbonate, anhydrous acid, sulfonate,dinitrile, 1,3-propanesultone, diphenyl disulfide, cyclohexylbenzene,biphenyl, fluorobenzene, t-butylbenzene (including the derivativesthereof).

Furthermore, the nonaqueous electrolyte liquid used in the nonaqueouselectrolyte secondary battery can further include a gelatification agentconventionally known, such as a polymer, thereby making the nonaqueouselectrolyte liquid in a gel state (i.e., gelled electrolyte).

[Nonaqueous Electrolyte Secondary Battery]

The embodiment of the nonaqueous electrolyte secondary battery of thepresent invention is not particularly limited. For example, it can beprovided in any form including a small size embodiment such ascylindrical form, coin form, button form, flat form and rectangularform, and a large size embodiment for e.g., electric vehicles.

In addition, after assembled into an embodiment of the nonaqueouselectrolyte secondary battery an activation process is generally appliedto making it into a condition for shipment. The activation processmainly includes initial charge process or aging process. Through theactivation process, there is a tendency that the densities of thepositive electrode composition layer and the negative electrodecomposition layer are decreased by absorption of the nonaqueouselectrolyte or migration of Li ions. Generally, the density of thepositive electrode composition layer is decreased by 3 to 10%approximately, and the density of the negative electrode compositionlayer is decreased by 10 to 20% approximately.

In Example 1 as discussed later, for example, the density of thepositive electrode composition layer was 3.95 g/cm³ at the time when theelectrode was prepared. However, a battery assembled was applied to tencycles of charge and discharge and the electrode was taken out, andthen, the density of the positive electrode composition layer wasmeasured. At that time, the density was by 3.77 g/cm³, finding adecrease compared with the density when the electrode was prepared.

Also, in Example 1 discussed later, the positive electrode taken outafter applying ten cycles of charge and discharge had a capacity densityof the positive electrode composition layer per unit volume (i.e.,energy density of the positive electrode composition layer) of 2.71Wh/cm³.

In summary, the density of the positive electrode composition layer atthe time when the electrode was prepared was 3.95 g/cm³. The density ofthe positive electrode composition layer in the battery after 10 cyclesof charge and discharge was 3.7 g/cm³. The energy density of thepositive electrode composition layer was 2.7 Wh/cm³ or more.

The nonaqueous electrolyte secondary battery of the present inventioncan be used by setting the charge stop voltage at around 4.2V in thesame manner as conventional nonaqueous electrolyte secondary batteries.However, it can be used in a charge method by setting the charge stopvoltage at a level more than the above, that is, 4.3V or more. Even ifit is charged by the method above to be exposed at a high temperature,good charge discharge cycle characteristic and storage properties can bemaintained. However, it is preferable that the charge stop voltage incharging the nonaqueous electrolyte secondary battery is 4.6V or less.

The nonaqueous electrolyte secondary battery of the present inventioncan be used as the same applications as those of conventionally knownnonaqueous electrolyte secondary batteries. According to the presentinvention, since the density of the positive electrode composition layeris high, the properties of high capacity and energy density per volumecan be improved. Therefore, significant effects can be given inapparatus which requires a high capacity in a limited volume, such asmobile device, small size apparatus, and robot application in which manybatteries are assembled in series.

EXAMPLES

Hereinafter, the present invention is described in more detail based onthe examples. It is, however, noted that the following examples shouldnot be used to narrowly construe the scope of the present invention.

Example 1

<Preparation of Positive Electrode>

LiCoO₂ particles having an average particle diameter of 5 μm and LiCoO₂particles having an average particle diameter of 27 μm were mixed at aratio (mass ratio) at 15:85 to obtain a positive electrode activematerial for preparing a positive electrode. 96 parts by mass of thepositive electrode material above, 20 parts by mass of an NMP solutioncontaining PVDF as a binder at a concentration of 10 mass %, and 1 partby mass of artificial graphite and 1 part by mass of ketjen black asconductive assistants were kneaded with a twin screw extruder, intowhich an NMP was further added to adjust a viscosity, so as to prepare apositive electrode composition containing paste.

The positive electrode composition containing paste above was applied onone surface of an aluminum foil (i.e., positive electrode currentcollector) having a thickness of 12 μm at an application quantity of27.7 mg/cm². A dry furnace having two dryers was used, one dryer at theupstream side being set at 115° C., and the other dryer at thedownstream side being set at 125° C. Thereby, a positive electrodecomposition layer was obtained by drying. The other surface of thealuminum foil was treated in the same manner, thereby forming positiveelectrode composition layers on both surfaces of the aluminum foil.Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil, thereby obtaining a positive electrode having abelt-shape with a length of 1,000 mm and a width of 54 mm. The positiveelectrode composition layer of the positive electrode obtained above hada density of 3.96 g/cm³ and a thickness of 70 μm in each surface.

<Preparation of Negative Electrode>

97.5 parts by mass of a negative electrode active material, i.e., amixture of MCMB (average particle diameter 20 μm) and natural graphite(average particle diameter 20 μm) at a mass ratio of 6:4; 1.5 parts bymass of SBR as a binder; and 1 part by mass of CMC as a thickening agentwere added into water for mixing, so as to prepare a negative electrodecomposition containing paste.

The negative electrode composition containing paste was applied on bothsurfaces of a copper foil (i.e., a negative electrode current collector)having a thickness of 8 μm, and then, dried at 120° C. for 12 hours invacuum to obtain a negative electrode composition layer having formed onboth surfaces of the copper foil (note that it has formed partly on onesurface thereof). Then, a calendar process was applied so that thethickness and the density of the negative electrode composition layerwere controlled. Then, a negative electrode current collector tab madeof nickel was welded on the exposed part of the copper foil, therebyobtaining a negative electrode having a belt-shape with a length of 990mm and a width of 55 mm. The negative electrode composition layer of thenegative electrode obtained above had a density of 1.65 g/cm³ and athickness of 86 μm in each surface.

<Preparation of Nonaqueous Electrolyte Liquid>

Into a mixture solvent of ethylene carbonate and diethyl carbonate at avolume ratio of 3:7, LiPF₆ was dissolved at a concentration of 1.1mol/L, and then, 2 mass % of vinylene carbonate and 2 mass % offluoroethylene carbonate were added therein to prepare a nonaqueouselectrolyte.

<Preparation of Separator>

Into 5 kg of boehmite having an average particle diameter d50 of 1 μm, 5kg of ion exchanged water and 0.5 kg of dispersant (i.e., aqueous typeammonium polycarboxylate having a solid content concentration of 40 mass%) were added. Then, a milling process was carried out in a ball millhaving an internal volume of 20 L at a rotation rate of 40 times/min for10 hours, thereby obtaining a dispersion liquid. The dispersion liquidobtained after the process above was dried in vacuum at 120° C. Anobservation by SEM confirmed that the shape of the boehmite wasapproximately plate-shaped.

Into 500 g of the dispersion liquid above, 0.5 g of xanthan gum as athickening agent, and 17 g of a resin binder dispersion as a binder(i.e., denatured polybutyl acrylate having a solid content of 45 mass %)were added, which were then stirred with a three-one motor for threehours to obtain a homogeneous slurry [i.e., a slurry for preparing aheat-resistant porous layer (II) having a solid content ratio of 50 mass%].

Onto one surface of a PE fine porous separator for nonaqueouselectrolyte secondary batteries [i.e., a resin porous layer (I) having athickness of 18 μm, a cavity rate of 40% and an average pore diameter of0.08 μm, in which the melting temperature of PE is 135° C.], a coronadischarge process (at an electric discharge amount of 40 W min/m²) wasapplied. Onto the processed surface above, the slurry for preparing theheat-resistant porous layer (II) was applied by means of a micro gravurecoater, and dried, so as to form a heat-resistant porous layer (II)having a thickness of 4 μm. As a result, a laminate type separator wasobtained. The mass per unit area of the heat-resistant porous layer (II)of this separator was 5.5 g/m², and the volume content of the boehmitewas 95 volume %, and the cavity rate was 45%.

<Assembling of Battery>

The positive electrode having the belt-shaped and the negative electrodehaving the belt-shaped, as explained before, were stacked withintervention of the laminate type separator also discussed above suchthat the heat-resistant porous layer (II) is located at the side of thepositive electrode, which was then wound in eddy form. Then, thecross-section thereof was pressed to make it flattened to obtain aflat-shaped winding electrode body. This winding electrode body wasfixed with an insulating tape made of polypropylene. Then, the windingelectrode body was inserted into a battery case having a prism shapemade of aluminum alloy. A lead part was welded thereto, and a lid platemade of aluminum alloy was welded to the opening end of the batterycase. Then, a nonaqueous electrolyte liquid was injected from theinjection hole provided on the lid plate, and kept still for one hour.Then, the injection hole was sealed. As a result, there was obtained anonaqueous electrolyte secondary battery having a structure shown inFIG. 1 with an appearance shown in FIG. 2.

The nonaqueous electrolyte secondary battery is then explained withreference to FIG. 1 and FIG. 2. FIG. 1 is a partial cross-sectional viewthereof. The positive electrode 1 and the negative electrode 2 werewound into an eddy form with intervention of the separator 3, followedby being pressed into a flat shape to form a flat-shaped windingelectrode body 6, and then, housed inside the battery case 4 having aprism shape (i.e., prism barrel shape) along with a nonaqueouselectrolyte liquid. However, to avoid complicatedness, FIG. 1 does notillustrate the metal foil as a current collector used in preparation ofthe positive electrode 1 and the negative electrode 2 as well as thenonaqueous electrolyte liquid.

The battery case 4 is made of aluminum alloy, constituting the exteriorbody of the battery. This exterior can 4 serves as a positive terminal.Also, an insulator 5 made of a PE sheet is placed on the bottom ofbattery case 4. The positive electrode 1, the negative electrode 2 andthe separator 3 constitute the flat-shaped winding electrode body 6,from which a positive electrode lead body 7 and a negative electrodelead body 8 are drawn, each end thereof being connected to the positiveelectrode 1 and the negative electrode 2. In addition, the lid plate 9for sealing made of aluminum alloy is intended to close the opening ofthe battery case 4. The lid plate 9 is attached to the terminal 11 madeof stainless steel via a packing 10 made of PP. To the terminal 11, alead board 13 made of stainless steel is attached via an insulator 12.

Also, the lid plate 9 was inserted in the opening of the battery case 4,and the joint part has been welded to each other, thereby closing theopening of the battery case 4, and therefore, the battery inside wassealed. In addition, in case of the battery shown in FIG. 1, aninjection hole 14 for the nonaqueous electrolyte liquid is provided atthe lid plate 9. This injection hole 14 for the nonaqueous electrolyteliquid is inserted with a sealing material, and then, sealed by weldingby means of, for example, laser welding. As a result, the battery issecured to be sealed. Furthermore, in order to provide a mechanism toexhaust internal gases to the outside when the temperature of thebattery is raised, the lid plate 9 is provided with a cleavage vent 15.

In the battery of Example 1, the positive electrode lead body 7 has beendirectly welded to the lid plate 9 so that the battery case 4 and thelid plate 9 function as a positive terminal. Also, the negativeelectrode lead body 8 has been welded to the lead board 13, so that thenegative electrode lead body 8 is electrically connected to the terminal11 via the lead board 13 such that the terminal 11 function as anegative electrode terminal. However, depending on the material ofbattery case 4, the positive or negative can be reversely provided.

FIG. 2 is a perspective view schematically showing the appearance of thebattery of FIG. 1. FIG. 2 is illustrated for the purpose to show thatthe battery was a prism shape battery. It is noted that the battery inFIG. 1 is illustrated schematically, and several selective components ofthe constitution components of the battery are illustrated. It is alsonoted in FIG. 1 that the inner part of the winding electrode body doesshow its cross-sectional view. Also, the layers of the separator are notdistinguishably illustrated.

Example 2

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then was applied onone surface of an aluminum foil (i.e., positive electrode currentcollector) having a thickness of 12 μm at an application quantity of27.7 mg/cm². A dry furnace having two dryers was used, one dryer at theupstream side being set at 115° C., and the other dryer at thedownstream side being set at 125° C. Thereby, a positive electrodecomposition layer was obtained by drying. The other surface of thealuminum foil was treated in the same manner, thereby forming positiveelectrode composition layers on both surfaces of the aluminum foil.Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil, thereby obtaining a positive electrode having abelt-shape with a length of 1,000 mm and a width of 54 mm. The positiveelectrode composition layer of the positive electrode obtained above hada density of 4.02 g/cm³ and a thickness of 69 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Example 3

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm at an application quantity of 27.5 mg/cm². Adry furnace having two dryers was used, one dryer at the upstream sidebeing set at 115° C., and the other dryer at the downstream side beingset at 125° C. Thereby, a positive electrode composition layer wasobtained by drying. The other surface of the aluminum foil was treatedin the same manner, thereby forming positive electrode compositionlayers on both surfaces of the aluminum foil. Then, a calendar processwas applied in which by adjusting the condition, the thickness and thedensity of the positive electrode composition layer were controlled.Then, a positive electrode current collector tab made of aluminum waswelded on the exposed part of the aluminum foil of the positiveelectrode, thereby obtaining a positive electrode having a belt-shapewith a length of 1,000 mm and a width of 54 mm. The positive electrodecomposition layer of the positive electrode obtained above had a densityof 4.11 g/cm³ and a thickness of 67 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Example 4

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm. A dry furnace having two dryers was used,one dryer at the upstream side being set at 100° C., and the other dryerat the downstream side being set at 125° C. Thereby, a positiveelectrode composition layer was obtained by drying. The other surface ofthe aluminum foil was treated in the same manner, thereby formingpositive electrode composition layers on both surfaces of the aluminumfoil. Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil, thereby obtaining a positive electrode having abelt-shape with a length of 1,000 mm and a width of 54 mm. The positiveelectrode composition layer of the positive electrode obtained above hada density of 3.96 g/cm³ and a thickness of 70 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Example 5

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm. A dry furnace having two dryers was used,one dryer at the upstream side being set at 100° C., and the other dryerat the downstream side being set at 125° C. Thereby, a positiveelectrode composition layer was obtained by drying. The other surface ofthe aluminum foil was treated in the same manner, thereby formingpositive electrode composition layers on both surfaces of the aluminumfoil. Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil, thereby obtaining a positive electrode having abelt-shape with a length of 1,000 mm and a width of 54 mm. The positiveelectrode composition layer of the positive electrode obtained above hada density of 4.02 g/cm³ and a thickness of 69 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Example 6

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm. A dry furnace having two dryers was used,one dryer at the upstream side being set at 100° C., and the other dryerat the downstream side being set at 125° C. Thereby, a positiveelectrode composition layer was obtained by drying. The other surface ofthe aluminum foil was treated in the same manner, thereby formingpositive electrode composition layers on both surfaces of the aluminumfoil. Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil, thereby obtaining a positive electrode having abelt-shape with a length of 1,000 mm and a width of 54 mm. The positiveelectrode composition layer of the positive electrode obtained above hada density of 4.11 g/cm³ and a thickness of 67 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Example 7

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm. A dry furnace having two dryers was used,one dryer at the upstream side being set at 90° C., and the other dryerat the downstream side being set at 125° C. Thereby, a positiveelectrode composition layer was obtained by drying. The other surface ofthe aluminum foil was treated in the same manner, thereby formingpositive electrode composition layers on both surfaces of the aluminumfoil. Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil, thereby obtaining a positive electrode having abelt-shape with a length of 1,000 mm and a width of 54 mm. The positiveelectrode composition layer of the positive electrode obtained above hada density of 3.96 g/cm³ and a thickness of 70 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Example 8

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm. A dry furnace having two dryers was used,one dryer at the upstream side being set at 90° C., and the other dryerat the downstream side being set at 125° C. Thereby, a positiveelectrode composition layer was obtained by drying. The other surface ofthe aluminum foil was treated in the same manner, thereby formingpositive electrode composition layers on both surfaces of the aluminumfoil. Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil, thereby obtaining a positive electrode having abelt-shape with a length of 1,000 mm and a width of 54 mm. The positiveelectrode composition layer of the positive electrode obtained above hada density of 4.02 g/cm³ and a thickness of 69 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Example 9

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm. A dry furnace having two dryers was used,one dryer at the upstream side being set at 90° C., and the other dryerat the downstream side being set at 125° C. Thereby a positive electrodecomposition layer was obtained by drying. The other surface of thealuminum foil was treated in the same manner, thereby forming positiveelectrode composition layers on both surfaces of the aluminum foil.Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil, thereby obtaining a positive electrode having abelt-shape with a length of 1,000 mm and a width of 54 mm. The positiveelectrode composition layer of the positive electrode obtained above hada density of 4.11 g/cm³ and a thickness of 67 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Example 10

<Preparation of Separator>

Into 5 kg of a plate-shaped boehmite (having an average particlediameter of 1 μm and an aspect ratio of 10), 5 kg of ion exchanged waterand 0.5 kg of dispersant (i.e., aqueous type ammonium polycarboxylatehaving a solid content concentration of 40 mass %) were added. Then, amilling process was carried out in a ball mill having an internal volumeof 20 L at a rotation rate of 40 times/min for 10 hours, therebyobtaining a dispersion liquid. A part of the dispersion liquid obtainedapplied after the process above was dried in vacuum at 120° C. Anobservation by SEM confirmed that the shape of the boehmite wasapproximately plate-shaped. Also, the average particle diameter of theboehmite applied after the process was 1 μm.

Into 500 g of the dispersion liquid above, 0.5 g of xanthan gum as athickening agent, and 17 g of a resin binder dispersion as a binder(i.e., denatured polybutyl acrylate having a solid content of 45 mass %)were added, which were then stirred with a three-one motor for threehours to obtain a homogeneous slurry for preparing a heat-resistantporous layer (II) (which had a solid content ratio of 50 mass %).

Onto one surface of a PE fine porous separator for nonaqueouselectrolyte secondary batteries, that is, a resineous porous layer (I),(which had a thickness of 10 μm, a cavity rate of 40% and an averagepore diameter of 0.08 μm, in which the melting temperature of PE is 135°C.), a corona discharge process (at an electric discharge amount of 40W·min/m²) was applied. Onto the processed surface above, the slurry forpreparing the heat-resistant porous layer (II) was applied by means of amicro gravure coater, and dried, so as to form a heat-resistant porouslayer (II) having a thickness of 2 μm. As a result, a laminate typeseparator was obtained.

Then, an acrylic acid (which included a solid content ratio of 20 mass%), that is, a delayed tack type adhesive resin as an adhesive resin(C), was provided. The acrylic acid was applied on both surfaces of thestacked product, that is, at the side of the resin porous layer (I) andat the side of heat-resistant porous layer (II) by means of a microgravure coater, and dried. As a result, there was obtained a separator(a thickness of 22 μm) with the adhesive resin (C) on the both surfaces.In addition, regarding this separator, the total area of the existencedomains of the adhesive resin (C) was determined, finding 30% of thearea of the surface where the adhesive resin (C) of the separatorexists. The targeted application weight of the adhesive resin (C) was0.5 g/m².

<Assembling of Battery>

The separator as obtained above was stacked between the positiveelectrode prepared in accordance with Example 1 and the negativeelectrode prepared in accordance with Example 1, and then wound in eddyform to obtain a winding electrode body. Then, the winding electrodebody was pressed to make its cross-section flat-shaped, followed byapplying a heat press process at 80° C. for one minute at a pressure of0.5 Pa to obtain a flat-shaped winding electrode body.

Except for using the flat-shaped winding electrode body explained here,the same procedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Example 11

The separator prepared in the same manner as Example 10 was provided,which was stacked between the positive electrode prepared in accordancewith Example 2 and the negative electrode prepared in accordance withExample 1, and then wound in eddy form to obtain a winding electrodebody. Then, the winding electrode body was pressed to make itscross-section flat-shaped, followed by applying a heat press process at80° C. for one minute at a pressure of 0.5 Pa to obtain a flat-shapedwinding electrode body.

Except for using the flat-shaped winding electrode body explained here,the same procedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Example 12

The separator prepared in the same manner as Example 10 was provided,which was stacked between the positive electrode prepared in accordancewith Example 3 and the negative electrode prepared in accordance withExample 1, and then wound in eddy form to obtain a winding electrodebody. Then, the winding electrode body was pressed to make itscross-section flat-shaped, followed by applying a heat press process at80° C. for one minute at a pressure of 0.5 Pa to obtain a flat-shapedwinding electrode body.

Except for using the flat-shaped winding electrode body explained here,the same procedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Comparative Example 1

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm. A dry furnace having two dryers was used,one dryer at the upstream side being set at 120° C., and the other dryerat the downstream side being set at 125° C. Thereby, a positiveelectrode composition layer was obtained by drying. The other surface ofthe aluminum foil was treated in the same manner, thereby formingpositive electrode composition layers on both surfaces of the aluminumfoil. Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil of the positive electrode, thereby obtaining a positiveelectrode having a belt-shape with a length of 1,000 mm and a width of54 mm. The positive electrode composition layer of the positiveelectrode obtained above had a density of 3.96 g/cm³ and a thickness of70 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Comparative Example 2

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm. A dry furnace having two dryers was used,one dryer at the upstream side being set at 125° C., and the other dryerat the downstream side being set at 125° C. Thereby a positive electrodecomposition layer was obtained by drying. The other surface of thealuminum foil was treated in the same manner, thereby forming positiveelectrode composition layers on both surfaces of the aluminum foil.Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil, thereby obtaining a positive electrode having abelt-shape with a length of 1,000 mm and a width of 54 mm. The positiveelectrode composition layer of the positive electrode obtained above hada density of 3.95 g/cm³ and a thickness of 70 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Comparative Example 3

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm. A dry furnace having two dryers was used,one dryer at the upstream side being set at 125° C., and the other dryerat the downstream side being set at 125° C. Thereby, a positiveelectrode composition layer was obtained by drying. The other surface ofthe aluminum foil was treated in the same manner, thereby formingpositive electrode composition layers on both surfaces of the aluminumfoil. Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil, thereby obtaining a positive electrode having abelt-shape with a length of 1,000 mm and a width of 54 mm. The positiveelectrode composition layer of the positive electrode obtained above hada density of 4.02 g/cm³ and a thickness of 69 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Comparative Example 4

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm. A dry furnace having two dryers was used,one dryer at the upstream side being set at 125° C., and the other dryerat the downstream side being set at 125° C. Thereby, a positiveelectrode composition layer was obtained by drying. The other surface ofthe aluminum foil was treated in the same manner, thereby formingpositive electrode composition layers on both surfaces of the aluminumfoil. Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil, thereby obtaining a positive electrode having abelt-shape with a length of 1,000 mm and a width of 54 mm. The positiveelectrode composition layer of the positive electrode obtained above hada density of 4.11 g/cm³ and a thickness of 67 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Comparative Example 5

The separator prepared in the same manner as Example 10 was provided,which was stacked between the positive electrode prepared in accordancewith Comparative Example 2 and the negative electrode prepared inaccordance with Example 1, and then wound in eddy form to obtain awinding electrode body. Then, the winding electrode body was pressed tomake its cross-section flat-shaped, followed by applying a heat pressprocess at 80° C. for one minute at a pressure of 0.5 Pa to obtain aflat-shaped winding electrode body.

Except for using the flat-shaped winding electrode body explained here,the same procedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Comparative Example 6

The separator prepared in the same manner as Example 10 was provided,which was stacked between the positive electrode prepared in accordancewith Comparative Example 3 and the negative electrode prepared inaccordance with Example 1, and then wound in eddy form to obtain awinding electrode body. Then, the winding electrode body was pressed tomake its cross-section flat-shaped, followed by applying a heat pressprocess at 80° C. for one minute at a pressure of 0.5 Pa to obtain aflat-shaped winding electrode body.

Except for using the flat-shaped winding electrode body explained here,the same procedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Comparative Example 7

The separator prepared in the same manner as Example 10 was provided,which was stacked between the positive electrode prepared in accordancewith Comparative Example 4 and the negative electrode prepared inaccordance with Example 1, and then wound in eddy form to obtain awinding electrode body. Then, the winding electrode body was pressed tomake its cross-section flat-shaped, followed by applying a heat pressprocess at 80° C. for one minute at a pressure of 0.5 Pa to obtain aflat-shaped winding electrode body.

Except for using the flat-shaped winding electrode body explained here,the same procedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Example 13

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm at an application quantity of 25.0 mg/cm². Adry furnace having two dryers was used, one dryer at the upstream sidebeing set at 115° C., and the other dryer at the downstream side beingset at 125° C. Thereby, a positive electrode composition layer wasobtained by drying. The other surface of the aluminum foil was treatedin the same manner, thereby forming positive electrode compositionlayers on both surfaces of the aluminum foil. Then, a calendar processwas applied in which by adjusting the condition, the thickness and thedensity of the positive electrode composition layer were controlled.Then, a positive electrode current collector tab made of aluminum waswelded on the exposed part of the aluminum foil, thereby obtaining apositive electrode having a belt-shape with a length of 1,100 mm and awidth of 54 mm. The positive electrode composition layer of the positiveelectrode obtained above had a density of 3.96 g/cm³ and a thickness of63 μm in each surface.

There was provided the negative electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on bothsurfaces of a copper foil (i.e., a negative electrode current collector)having a thickness of 8 μm, and then, dried at 120° C. for 12 hours invacuum to obtain a negative electrode composition layer having formed onboth surfaces of the copper foil (note that it has formed partly on onesurface thereof). Then, a calendar process was applied so that thethickness and the density of the negative electrode composition layerwere controlled. Then, a negative electrode current collector tab madeof nickel was welded on the exposed part of the copper foil, therebyobtaining a negative electrode having a belt-shape with a length of1,090 mm and a width of 55 mm. The negative electrode composition layerof the negative electrode obtained above had a density of 1.65 g/cm³ anda thickness of 81 μm in each surface.

Except for using the positive electrode and the negative electrodeexplained here, the same procedure as Example 1 was carried out toprepare a nonaqueous electrolyte secondary battery.

Example 14

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm at an application quantity of 22.9 mg/cm². Adry furnace having two dryers was used, one dryer at the upstream sidebeing set at 115° C., and the other dryer at the downstream side beingset at 125° C. Thereby, a positive electrode composition layer wasobtained by drying. The other surface of the aluminum foil was treatedin the same manner, thereby forming positive electrode compositionlayers on both surfaces of the aluminum foil. Then, a calendar processwas applied in which by adjusting the condition, the thickness and thedensity of the positive electrode composition layer were controlled.Then, a positive electrode current collector tab made of aluminum waswelded on the exposed part of the aluminum foil, thereby obtaining apositive electrode having a belt-shape with a length of 1,200 mm and awidth of 54 mm. The positive electrode composition layer of the positiveelectrode obtained above had a density of 3.95 g/cm³ and a thickness of58 μm in each surface.

There was provided the negative electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on bothsurfaces of a copper foil (i.e., a negative electrode current collector)having a thickness of 8 μm, and then, dried at 120° C. for 12 hours invacuum to obtain a negative electrode composition layer having formed onboth surfaces of the copper foil (note that it has formed partly on onesurface thereof). Then, a calendar process was applied so that thethickness and the density of the negative electrode composition layerwere controlled. Then, a negative electrode current collector tab madeof nickel was welded on the exposed part of the copper foil, therebyobtaining a negative electrode having a belt-shape with a length of1,190 mm and a width of 55 mm. The negative electrode composition layerof the negative electrode obtained above had a density of 1.65 g/cm³ anda thickness of 74 μm in each surface.

Except for using the positive electrode and the negative electrodeexplained here, the same procedure as Example 1 was carried out toprepare a nonaqueous electrolyte secondary battery.

Comparative Example 8

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm at an application quantity of 25.0 mg/cm². Adry furnace having two dryers was used, one dryer at the upstream sidebeing set at 125° C., and the other dryer at the downstream side beingset at 125° C. Thereby, a positive electrode composition layer wasobtained by drying. The other surface of the aluminum foil was treatedin the same manner, thereby forming positive electrode compositionlayers on both surfaces of the aluminum foil. Then, a calendar processwas applied in which by adjusting the condition, the thickness and thedensity of the positive electrode composition layer were controlled.Then, a positive electrode current collector tab made of aluminum waswelded on the exposed part of the aluminum foil, thereby obtaining apositive electrode having a belt-shape with a length of 1,100 mm and awidth of 54 mm. The positive electrode composition layer of the positiveelectrode obtained above had a density of 3.96 g/cm³ and a thickness of63 μm in each surface.

There was provided the negative electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on bothsurfaces of a copper foil (i.e., a negative electrode current collector)having a thickness of 8 μm, and then, dried at 120° C. for 12 hours invacuum to obtain a negative electrode composition layer having formed onboth surfaces of the copper foil (note that it has formed partly on onesurface thereof). Then, a calendar process was applied so that thethickness and the density of the negative electrode composition layerwere controlled. Then, a negative electrode current collector tab madeof nickel was welded on the exposed part of the copper foil, therebyobtaining a negative electrode having a belt-shape with a length of1,090 mm and a width of 55 mm. The negative electrode composition layerof the negative electrode obtained above had a density of 1.65 g/cm³ anda thickness of 81 μm in each surface.

Except for using the positive electrode and the negative electrodeexplained here, the same procedure as Example 1 was carried out toprepare a nonaqueous electrolyte secondary battery.

Comparative Example 9

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then was applied onone surface of an aluminum foil (i.e., positive electrode currentcollector) having a thickness of 12 μm at an application quantity of27.7 mg/cm². A dry furnace having two dryers was used, one dryer at theupstream side being set at 125° C., and the other dryer at thedownstream side being set at 125° C. Thereby, a positive electrodecomposition layer was obtained by drying. The other surface of thealuminum foil was treated in the same manner, thereby forming positiveelectrode composition layers on both surfaces of the aluminum foil.Then, a calendar process was applied in which by adjusting thecondition, the thickness and the density of the positive electrodecomposition layer were controlled. Then, a positive electrode currentcollector tab made of aluminum was welded on the exposed part of thealuminum foil, thereby obtaining a positive electrode having abelt-shape with a length of 1,000 mm and a width of 54 mm. The positiveelectrode composition layer of the positive electrode obtained above hada density of 3.8 g/cm³ and a thickness of 73 μm in each surface.

Except for using the positive electrode explained here, the sameprocedure as Example 1 was carried out to prepare a nonaqueouselectrolyte secondary battery.

Reference Example 1

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm at an application quantity of 21.2 mg/cm². Adry furnace having two dryers was used, one dryer at the upstream sidebeing set at 125° C., and the other dryer at the downstream side beingset at 115° C. Thereby, a positive electrode composition layer wasobtained by drying. The other surface of the aluminum foil was treatedin the same manner, thereby forming positive electrode compositionlayers on both surfaces of the aluminum foil. Then, a calendar processwas applied in which by adjusting the condition, the thickness and thedensity of the positive electrode composition layer were controlled.Then, a positive electrode current collector tab made of aluminum waswelded on the exposed part of the aluminum foil, thereby obtaining apositive electrode having a belt-shape with a length of 1,300 mm and awidth of 54 mm. The positive electrode composition layer of the positiveelectrode obtained above had a density of 3.8 g/cm³ and a thickness of56 μm in each surface.

There was provided the negative electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on bothsurfaces of a copper foil (i.e., a negative electrode current collector)having a thickness of 8 μm, and then, dried at 120° C. for 12 hours invacuum to obtain a negative electrode composition layer having formed onboth surfaces of the copper foil (note that it has formed partly on onesurface thereof). Then, a calendar process was applied so that thethickness and the density of the negative electrode composition layerwere controlled. Then, a negative electrode current collector tab madeof nickel was welded on the exposed part of the copper foil, therebyobtaining a negative electrode having a belt-shape with a length of1,290 mm and a width of 55 mm. The negative electrode composition layerof the negative electrode obtained above had a density of 1.65 g/cm³ anda thickness of 68 μm in each surface.

Except for using the positive electrode and the negative electrodeexplained here, the same procedure as Example 1 was carried out toprepare a nonaqueous electrolyte secondary battery.

Reference Example 2

There was provided the positive electrode composition containing pasteprepared in the same manner as Example 1, which was then applied on onesurface of an aluminum foil (i.e., positive electrode current collector)having a thickness of 12 μm at an application quantity of 21.2 mg/cm². Adry furnace having two dryers was used, one dryer at the upstream sidebeing set at 125° C., and the other dryer at the downstream side beingset at 125° C. Thereby, a positive electrode composition layer wasobtained by drying. The other surface of the aluminum foil was treatedin the same manner, thereby forming positive electrode compositionlayers on both surfaces of the aluminum foil. Then, a calendar processwas applied in which by adjusting the condition, the thickness and thedensity of the positive electrode composition layer were controlled.Then, a positive electrode current collector tab made of aluminum waswelded on the exposed part of the aluminum foil, thereby obtaining apositive electrode having a belt-shape with a length of 1,300 mm and awidth of 54 mm. The positive electrode composition layer of the positiveelectrode obtained above had a density of 3.8 g/cm³ and a thickness of56 μm in each surface.

Then, the positive electrode explained above and the negative electrodeprepared in the same procedure as Reference Example 2 were used. Unlessnoted here, the same procedure as Example 1 was carried out to prepare anonaqueous electrolyte secondary battery.

It is noted that Comparative Example 9 showed that when the currentdensity of the battery was high, the folding strength of the positiveelectrode could become deteriorated even if the density of the positiveelectrode composition layer was low. In addition, Reference Examples 1and 2 showed that when the current density of the battery was low, thefolding strength of the positive electrode could become high regardlessof the ratio a/b.

Various tests as showed below were carried out for evaluation withrespect to the nonaqueous electrolyte secondary batteries of theExamples, the Comparative Examples and the Reference Examples, as wellas the positive electrodes of them.

<Folding Strength of Positive Electrode>

Each nonaqueous electrolyte secondary batteries of the Examples, theComparative Examples and the Reference Examples were disassembled tocollect the positive electrodes. The part where the positive electrodecomposition layer was formed on both surfaces of the current collectorwas identified, and a test sample was cut out there to have a size of 5cm in the length direction and 4 cm in the width direction. The testsample was folded at a point of 15 mm from the edge of the lengthdirection in the same winding direction as preparing the windingelectrode body. Then, a load of 200 gf was uniformly applied at thefolding point of the test sample. Then, the test sample was stretched toopen, and the both ends of the test sample was held by a jig of atensile strength test equipment (“SDT-52” made by Imada SS Corporation).A tension test was carried out at a cross head speed 50 mm/m, and thestrength (N) when when the folding point of the test sample was brokenwas measured. The strength (N) was divided by 4 (cm) to calculate afolding strength (N/cm). As the folding strength becomes high, thebreakage of the positive electrode current collector of the flat-shapedwinding electrode body of the nonaqueous electrolyte secondary batteriescan be more favorably controlled, and therefore, a better evaluationregarding the productivity and the reliability of the nonaqueouselectrolyte secondary batteries can be given. The test results are shownin Table 1 and Table 3.

<Evaluation of Ratio a/b>

Each of the nonaqueous electrolyte secondary batteries of the Examples,the Comparative Examples and the Reference Examples was disassembled.With respect to the positive electrode of the winding electrode body, across-section at the center of the longitudinal direction of thepositive electrode composition layer at the internal side was decided asa target for analysis. The cross-section of the positive electrode wassubject to an ion milling processing to expose the surface. The sampleof the positive electrode thereby provided was observed by means of SEM(“S-3400N” made by Hitachi, Ltd.), and the elements were detected by EDX(Edax Japan Inc.) to carry out element mapping derived from the binder.

The observation conditions of the SEM were as follows: the accelerationvoltage was 15 kV, the magnification was 1,000 times, the pixel was512×400, and the stay time per unit area was 200 μsec. C (carbon) and F(fluorine) were selected, to observe them at total three points of thepositive electrode: two end points of the strip shaped positiveelectrode, and one point at the center thereof. A ratio a/b was obtainedat each point, and averaged value was calculated. These evaluationresults are shown in Tables 1 to 3.

<Occurrence of Breakage>

There were provided five samples of nonaqueous electrolyte secondarybatteries each prepared in accordance with Examples 1 to 3, 10 to 12 andComparative Example 2 to 4 and 5 to 7. From these batteries, aflat-shaped winding electrode body was collected and disassembled. Atthe folded portion of the most internal wounded part of the positiveelectrode, a sample was cut out to have a size of 5 cm in thelongitudinal direction and 4 cm in the width direction of the electrode.Then, the positive electrode as cut out above was again folded at thebent part, thereby making it folded into a half. A load of 10N wasuniformly applied for 3 seconds on the plane of such a folded state.Then, the folded positive electrode was opened, and the folded portionwas observed. Here, the convex portion along the folding line wasobserved to find whether the positive electrode was cut.

In the bending test, two samples were prepared from the positiveelectrode of each battery. In other words, 10 samples were tested ineach Example (or Comparative Example). Among the 10 samples, the numbersof the samples in which the positive electrode was cut were counted andshown in Table 2.

<Density of Post-10 Cycle Positive Electrode Composition Layer>

Each nonaqueous electrolyte secondary battery of the Examples, theComparative Examples and the Reference Examples was charged at aconstant current of 1.0 C at room temperature to reach 4.40V. Afterreached 4.40V, it was then charged at a constant voltage at 4.40V toreach an electric current of 0.05 C. Then, each battery was dischargedat a constant current of 1.0 C to reach a voltage of 3.0V. The series ofthe charge discharge operation above is assumed as one cycle, which wasrepeated 10 cycles. It is noted that a current value of 1.0 C means acurrent value which is able to discharge at a rating capacity in onehour.

Then, each battery was disassembled to collect the positive electrode,which was then washed with DEC and dried. The positive electrode afterdrying was cut out with a predetermined area, and its weight wasmeasured by using an electronic balance having a minimum scale of 1 mg.This weight was subtracted by the weight of the current collector,thereby producing the weight of the post-10 cycle positive electrodecomposition layer. Also, the total thickness of the post-10 cyclepositive electrode was measured at 10 points by using a micrometerhaving a smallest scale of 1 μm. The thickness of the current collectorwas subtracted from each total thickness as measured above, and theirresults were averaged. By using this average value and the area, thevolume of the post-10 cycle positive electrode composition layer wascalculated. A density of the post-10 cycle positive electrodecomposition layer was obtained by dividing the weight of the positiveelectrode composition layer by the volume. The results are shown inTables 1 to 3.

<Energy Density of Positive Electrode Composition Layer>

In the same condition as measuring the density of the post-10 cyclepositive electrode composition layer, there were provided nonaqueouselectrolyte secondary batteries of the Examples, the ComparativeExamples and the Reference Examples, each of which was disassembled tocollect the positive electrode. The positive electrode was cut out tohave a size of 2 cm² in which the positive electrode composition layerwas formed on one surface. A thickness was measured by using amicrometer to calculate the volume of the positive electrode compositionlayer alone as excluding the positive electrode current collector. Usinglithium as an opposite electrode, a model cell was prepared by using thenonaqueous electrolyte liquid same as used in the battery of Example 1.Each model cell was applied to a constant voltage charge at 0.05 C to4.50V, and after reaching 4.50V, it was applied to a constant voltagecharge at 4.50V to reach an electric current of 0.005 C. Then, eachmodel cell was discharged at a constant current of 0.05 C to reach 2.5V,and the discharge capacity at that time was obtained. The dischargeelectric power (i.e., discharge capacity times operating voltage) wascalculated. Then, the discharge electric power obtained was divided bythe volume of the positive electrode composition layer alone, so as toobtain an energy density (Wh/cm) of the positive electrode compositionlayer. The energy density of the positive electrode composition layerobtained was shown in Table 1 to Table 3.

<Current Density>

The positive electrode of each nonaqueous electrolyte secondary batteryof the Examples, the Comparative Examples and the Reference Examples wascollected. The total area of the positive electrode was measured byusing a ruler. Then, the current value (mA) of the 1.0 C of each batterywas divided by the total area (cm²) of the positive electrode, to obtaina current density (mA/cm²). The current density obtained is shown inTable 1 to Table 3.

TABLE 1 Density of the post-10 Energy Density of Folding cycle densityof the positive strength positive the positive electrode Existence ofthe electrode electrode composition of the positive compositioncomposition Current layer adhesive electrode layer layer density (g/cm³)layer a/b (N/cm) (g/cm³) (Wh/cm³) (mA/cm²) Example 1 3.96 None 2.1 14.33.77 2.71 4.58 Example 2 4.02 None 2.2 12.9 3.83 2.76 4.58 Example 34.11 None 2.1 9.5 3.91 2.82 4.58 Example 4 3.96 None 5.5 14.4 3.77 2.714.58 Example 5 4.02 None 5.1 14 3.83 2.76 4.58 Example 6 4.11 None 5.410.4 3.91 2.82 4.58 Example 7 3.96 None 10.5 14.2 3.77 2.71 4.58 Example8 4.02 None 11 13.9 3.83 2.76 4.58 Example 9 4.11 None 10.2 14 3.91 2.824.58 Comparative 3.96 None 1.6 4.6 3.77 2.71 4.58 Example 1 Comparative3.95 None 1.0 2.2 3.76 2.71 4.58 Example 2 Comparative 4.02 None 1.0 1.13.83 2.76 4.58 Example 3 Comparative 4.11 None 1.0 0 3.91 2.82 4.58Example 4

TABLE 2 Density of the post-10 Energy Density of cycle density of thepositive positive the positive electrode Existence Occurrence electrodeelectrode composition of the Of composition composition Current layeradhesive Breakage layer layer density (g/cm³) layer a/b (%) (g/cm³)(Wh/cm³) (mA/cm²) Example 1 3.96 None 2.1 0 3.77 2.71 4.58 Example 24.02 None 2.2 0 3.83 2.76 4.58 Example 3 4.11 None 2.1 0 3.91 2.82 4.58Comparative 3.95 None 1.0 1 3.76 2.71 4.58 Example 2 Comparative 4.02None 1.0 5 3.83 2.76 4.58 Example 3 Comparative 4.11 None 1.0  10 3.912.82 4.58 Example 4 Example 10 3.96 Yes 2.1 0 3.77 2.71 4.58 Example 114.02 Yes 2.2 0 3.83 2.76 4.58 Example 12 4.11 Yes 2.1 0 3.91 2.82 4.58Comparative 3.96 Yes 1.0 6 3.77 2.71 4.58 Example 5 Comparative 4.02 Yes1.0 9 3.83 2.76 4.58 Example 6 Comparative 4.11 Yes 1.0  10 3.91 2.824.58 Example 7

TABLE 3 Density of the post-10 Energy Density of Folding cycle densityof the positive strength positive the positive electrode Existence ofthe electrode electrode composition of the positive compositioncomposition Current layer adhesive electrode layer layer density (g/cm³)layer a/b (N/cm) (g/cm³) (Wh/cm³) (mA/cm²) Example 1 3.96 None 2.1 14.33.77 2.71 4.58 Example 13 3.96 None 2.1 16.4 3.77 2.71 4.24 Example 143.96 None 2.1 16.9 3.77 2.71 3.89 Comparative 3.96 None 1 5.5 3.77 2.714.24 Example 8 Comparative 3.80 None 1 4.1 3.62 2.61 4.58 Example 9Reference 3.80 None 2.1 17.8 3.62 2.61 3.6 Example 1 Reference 3.80 None1 15.7 3.62 2.61 3.6 Example 2

There are other embodiments than the description above without departingthe gist of the present invention. The embodiment described above is anexample, and the present invention is not limited to the embodiment. Thescope of the present invention should be construed primarily based onthe claims, not to the description of the specification or the presentapplication. Any changes within the ranges of the claims and theequivalence thereof should be construed as falling within the scope ofthe claims.

EXPLANATION OF THE REFERENCES IN THE DRAWINGS

-   -   1: Positive electrode;    -   2: Negative electrode; and    -   3: Separator.

What is claimed is: 1: A positive electrode for a nonaqueous electrolytesecondary battery, a folded portion formed at least at one part of thepositive electrode in an electrode body, the positive electrodecomprising a single first positive electrode composition layer on oneside of a positive electrode current collector, wherein the single firstpositive electrode composition layer comprises at least a positiveelectrode active material, a binder and a conductive assistant, whereinan energy density of the positive electrode composition layer after 10cycles of charge and discharge is 2.7 Wh/cm³ or more, wherein across-section of the single first positive electrode composition layerhas a domain A extending from a central part to a surface side in athickness direction thereof, and a domain B extending from the centralpart to the positive electrode current collector thereof, wherein thecentral part is located with equal distance in the thickness directionfrom the surface side and the positive electrode current collector,wherein the single first positive electrode composition layer has an a/bvalue of 2 or more, the a/b value being obtained in accordance with amethod comprising: a step of detecting elements derived from the binderby means of SEM-EDX with respect to the cross-section of the singlefirst positive electrode composition layer; a step of selecting a firstelement included in the binder at the highest quantity among theelements detected, and selecting a second element included in the binderat the second highest quantity among the elements detected; a step ofdrawing a first element mapping of the first element, and drawing asecond element mapping of the second element, the first element mappingbeing drawn in a vision field same as the second element mapping; and astep of calculating an area where the first element mapping overlapswith the second element mapping; wherein the method is carried out oneach the domain A and the domain B, a ratio of the area in the domain Ais defined as “a,” a ratio of the area in the domain B is defined as“b,” thereby obtaining the a/b value. 2: A positive electrode for anonaqueous electrolyte secondary battery, a folded portion formed atleast at one part of the positive electrode in an electrode body, thepositive electrode comprising a single first positive electrodecomposition layer on one side of a positive electrode current collector,wherein the single first positive electrode composition layer comprisesat least a positive electrode active material, a binder and a conductiveassistant, wherein a density of the positive electrode composition layerafter 10 cycles of charge and discharge is 3.7 g/cm³ or more, wherein across-section of the single first positive electrode composition layerhas a domain A extending from a central part to a surface side in athickness direction thereof, and a domain B extending from the centralpart to the positive electrode current collector thereof, wherein thecentral part is located with equal distance in the thickness directionfrom the surface side and the positive electrode current collector,wherein the single first positive electrode composition layer has an a/bvalue of 2 or more, the a/b value being obtained in accordance with amethod comprising: a step of detecting elements derived from the binderby means of SEM-EDX with respect to the cross-section of the singlefirst positive electrode composition layer; a step of selecting a firstelement included in the binder at the highest quantity among theelements detected, and selecting a second element included in the binderat the second highest quantity among the elements detected; a step ofdrawing a first element mapping of the first element, and drawing asecond element mapping of the second element, the first element mappingbeing drawn in a vision field same as the second element mapping; and astep of calculating an area where the first element mapping overlapswith the second element mapping; wherein the method is carried out oneach the domain A and the domain B, a ratio of the area in the domain Ais defined as “a,” a ratio of the area in the domain B is defined as“b,” thereby obtaining the a/b value. 3: The positive electrode for thenonaqueous electrolyte secondary battery according to claim 2, whereinthe density of the positive electrode composition layer after 10 cyclesof charge and discharge is 3.77 g/cm³ or more 4: The positive electrodefor the nonaqueous electrolyte secondary battery according to claim 2,wherein the density of the positive electrode composition layer after 10cycles of charge and discharge is 3.83 g/cm³ or more 5: The positiveelectrode for the nonaqueous electrolyte secondary battery according toclaim 2, wherein the density of the positive electrode composition layerafter 10 cycles of charge and discharge is 3.91 g/cm³ or more 6: Anonaqueous electrolyte secondary battery comprising: an electrode bodycomprising a positive electrode, a negative electrode, a separator; anda nonaqueous electrolyte, wherein an energy density of the positiveelectrode composition layer after 10 cycles of charge and discharge is2.7 Wh/cm³ or more, wherein the positive electrode comprises: a singlefirst positive electrode composition layer on one side of a positiveelectrode current collector; and a folded portion formed at least at onepart of the positive electrode, wherein the single first positiveelectrode composition layer comprises at least a positive electrodeactive material, a binder and a conductive assistant, wherein across-section of the single first positive electrode composition layerhas a domain A extending from a central part to a surface side in athickness direction thereof, and a domain B extending from the centralpart to the positive electrode current collector thereof, wherein thecentral part is located with equal distance in the thickness directionfrom the surface side and the positive electrode current collector,wherein the single first positive electrode composition layer has an a/bvalue of 2 or more, the a/b value being obtained in accordance with amethod comprising: a step of detecting elements derived from the binderby means of SEM-EDX with respect to the cross-section of the singlefirst positive electrode composition layer; a step of selecting a firstelement included in the binder at the highest quantity among theelements detected, and selecting a second element included in the binderat the second highest quantity among the elements detected; a step ofdrawing a first element mapping of the first element, and drawing asecond element mapping of the second element, the first element mappingbeing drawn in a vision field same as the second element mapping; and astep of calculating an area where the first element mapping overlapswith the second element mapping; wherein the method is carried out oneach the domain A and the domain B, a ratio of the area in the domain Ais defined as “a,” a ratio of the area in the domain B is defined as“b,” thereby obtaining the a/b value. 7: The nonaqueous electrolytesecondary battery according to claim 6, wherein the electrode body is awinding electrode body in which the positive electrode and the negativeelectrode are wound into in an eddy form with intervention of theseparator therebetween, wherein a cross cross-section of the electrodebody is flat-shaped. 8: The nonaqueous electrolyte secondary batteryaccording to claim 6, further comprising an adhesive layer at one orboth of a first border and a second border, the first border beingbetween the positive electrode and the separator, the second borderbeing between the negative electrode and the separator. 9: Thenonaqueous electrolyte secondary battery according to claim 8, whereinthe separator is provided with the adhesive layer at one side or bothsides thereof. 10: A nonaqueous electrolyte secondary batterycomprising: an electrode body comprising a positive electrode, anegative electrode, a separator; and a nonaqueous electrolyte, wherein adensity of the positive electrode composition layer after 10 cycles ofcharge and discharge is 3.7 g/cm³ or more, wherein the positiveelectrode comprises: a single first positive electrode composition layeron one side of a positive electrode current collector; and a foldedportion formed at least at one part of the positive electrode, whereinthe single first positive electrode composition layer comprises at leasta positive electrode active material, a binder and a conductiveassistant, wherein a cross-section of the single first positiveelectrode composition layer has a domain A extending from a central partto a surface side in a thickness direction thereof, and a domain Bextending from the central part to the positive electrode currentcollector thereof, wherein the central part is located with equaldistance in the thickness direction from the surface side and thepositive electrode current collector, wherein the single first positiveelectrode composition layer has an a/b value of 2 or more, the a/b valuebeing obtained in accordance with a method comprising: a step ofdetecting elements derived from the binder by means of SEM-EDX withrespect to the cross-section of the single first positive electrodecomposition layer; a step of selecting a first element included in thebinder at the highest quantity among the elements detected, andselecting a second element included in the binder at the second highestquantity among the elements detected; a step of drawing a first elementmapping of the first element, and drawing a second element mapping ofthe second element, the first element mapping being drawn in a visionfield same as the second element mapping; and a step of calculating anarea where the first element mapping overlaps with the second elementmapping; wherein the method is carried out on each the domain A and thedomain B, a ratio of the area in the domain A is defined as “a,” a ratioof the area in the domain B is defined as “b,” thereby obtaining the a/bvalue. 11: The nonaqueous electrolyte secondary battery according toclaim 10, wherein the density of the positive electrode compositionlayer after 10 cycles of charge and discharge is 3.77 g/cm³ or more 12:The nonaqueous electrolyte secondary battery according to claim 10,wherein the density of the positive electrode composition layer after 10cycles of charge and discharge is 3.83 g/cm³ or more 13: The nonaqueouselectrolyte secondary battery according to claim 10, wherein the densityof the positive electrode composition layer after 10 cycles of chargeand discharge is 3.91 g/cm³ or more. 14: The nonaqueous electrolytesecondary battery according to claim 10, wherein the electrode body is awinding electrode body in which the positive electrode and the negativeelectrode are wound into in an eddy form with intervention of theseparator therebetween, wherein a cross cross-section of the electrodebody is flat-shaped. 15: The nonaqueous electrolyte secondary batteryaccording to claim 10, further comprising an adhesive layer at one orboth of a first border and a second border, the first border beingbetween the positive electrode and the separator, the second borderbeing between the negative electrode and the separator. 16: Thenonaqueous electrolyte secondary battery according to claim 15, whereinthe separator is provided with the adhesive layer at one side or bothsides thereof.